I want to speak about the first ever RPG I ever played. Partially due to nostalgia, partially because nobody else seem to remember it and partially because I believe there was a (small) number of interesting things which might be useful to DIY people.
To keep an extremely long backstory short(er) it is enough to say that this game was developed in as much of informational vacuum as it was possible in pre- and early post-Iron Curtain world. The title game, 'The Enchanted Country' itself was, as far as I know, an imprecise translation of a Polish board game of the same name, which in turn was a vague, distant reinterpretation of one of earliest editions DnDs, one of those where class and race were still combined into one.
Said informational vacuum was, at the beginning, very tight: imagine a place where the whole idea of fantasy literature was almost entirely limited to mythology, folk tales, children tales such as 'Peppy Longstocking', 'Alice in Wonderland' and a sequel, a retelling of 'Wizard of Oz', and some Gothic tales such as 'Melmoth the Wanderer'. Until certain point not only the state had a very dim view on what was ok to publish (very few western things, usually censored as well) but good books themselves were very hard to find physically. Later it changed and sometime later the floodgates got tossed open, but for a some time idea of RPGs as community or as evolving movement or even as something that wasn't just our game was unknown to us.
When I got to the game it was already heavily reworked from the board game, and all major features described below already in place although the improvement process never stopped. The author, who's name, I believe, was Ephraim, took a board game based on DnD and kind of reverse engineered it back to DnD, probably without knowledge about RPGs in general.
So what I think was interesting about it:
1) The world/setting itself had three defined ages, each with its own map; first two ended in big ruinations, third one was kind of open-ended. First age, Yord, was built on Scandinavian Eddas, second, Theargund, was closer to mainstream fantasy, with Tolkien, Moorcock, Vance and, later, Dragonlance first trilogy as main influences; third age was Feralard, kind of postapocalyptic magitech closest to 'Wheel of Time'. The whole cosmos ran on a mix of Buddhist, Zoroastrian and cabbalistic principles, in which those ages were but a least physical emanation of something much greater.
All ages/settings were a bit 'magpie' in sense that whatever cool new book the author read had contributed to the whole, although the author exercised discretion (so we had no dedicated ninja class or culture). 'Wheel of time' was the most interesting case because despite coming very late, it already worked very well with the whole underlying structure. Certain metanarrative run through all ages where Morgoth was the same Dark One in The Bore, Surt was Gotmog, and Valars lived in Asgard later renamed Valinor after their first generation was killed off. It sounds a bit strange now, but the author was really good at building this kind of intertwined lore.
In practical sense three ages allowed free and fun time-travel. For example there was a bunch of people who needed somebody to go to Yord and snatch something before Ragnarok hits it; once I got petrified and got awoken in Feralard, and so on. Cities became dungeons, dungeons became cities, places appeared and vanished, but every change was visible and could have been practically used.
Different homerules could be applied to each age as well, as a decay and a progress changed things.
2) Map movement was in squares, but the movement speed was always the same - on a more difficult terrains such as mountains those squares were drawn much smaller than on plains and roads, so the travel through those areas took more time. On a plus side, it gone away with remembering how much each terrain impeded the travel.
3.1) Magic was a simple coding language. The base unit was 'true name' rune of a basic element of universe such as 'ring', 'fire', 'iron', etc; those runes were assembled in a linear formula which was a spell. Almost all spells started with either 'on me' or 'from me' rune of direction, specifying inward or outward application; without them magic affected everything around. There were no operators of conditions or of cycles, no branching, no GO TO, but runes could be subjugated to one another to mean new things, such as 'ring (fire)' meant ring of fire, and ring(fire(man)) could mean ring of passion as new things built by such subjugations were judged mostly as kennings, in a poetic, not literal sense, and 'grass of battle' might have meant bones.
There was total of about fifty or so runes and you could develop your own spells. For the latter there was no defined system, and DM basically assigned numbers/levels based on how much power the desired effect would give. I do recall that one 5th level character who became a Buddha by learning true name of the world due to very clever magic coding.
3.2) The magic was different age to age, and various types of magic were initially open only to certain groups, especially in Yord - only non-playable races such as jotunns wielded fire and ice magic, for example, while only playable alfar and zwergs wielded air and stone powers. Humans didn't have any magic (except demonology and such) until Theargund when black, white and red magic were developed; Feralard saw a 'unified field of magic' approach where lines were first blurred and then eliminated.
This approach didn't only affect the kind of powers but their severity as well. Many high-impact powers in Yord, such as teleport, raise dead and so on, were number per life cast, i.e. through all life of the character you could only cast raise dead about five times (and you cannot cheat by killing yourself to reset the count). As history moved forward such powers became number per year and later numbe per month or even per day which drastically changed their application and the face of the world.
Not speaking of Feralard and its unified magic, spells were a few per type of magic, with full type of magic maybe having total of 25-30 - in that respect they were similar to Spheres like they were in 2nd edition (only nobody knew about 2nd edition back then). Each new spell-level a mage would get about three to five new spells in their chosen type of magic and those were all that this type of magic had on this level so the mage had an immediate access to all spells of their chosen type a bit like clerics in actual DnD did. In Yord this was the end of it but in Theargund you could learn some spells from other types of magic although not much. Demonologists, necromancers and certain other classes such as witchers had their own subsystems, usually with not so grandiose higher-level effects effects.
There was no memorization, but each spell had an attached number of how many times per day/month/year/life it could be cast, and in this sense spells were countable resources more than free abilities of a character, although there was also magic point system that complicated this by further limiting amount of how many spells a mage could cast every day in general. For example, if the air magic invisibility was 2/week casting, a mage could only cast it twice per lunar week regardless of how much magic points they had left; on another hand, casting flaming lance (9/day type spell) could exhaust reserves of power before the mage met the attached spell limit.
4) In a casting of spell all runes had to be actually pronounced aloud with proper pauses and emphasis, and the magical mishap was embedded directly into this procedure because no matter how much you train, you can and will eventually mispronounce something. In a such case the mispronounced rune was then taken off the equation, and DM judged what new formula did, usually with some additional detrimental effect. Of course, each kind of magic (especially in Yord) has its own sounding system and dwarven, for example, was full of very difficult sounds and was a pain to speak.
All highest-level spells had snappy names built on consonance: top black magic spell was called 'Pike of Darkness' but it sounded more like 'Disk of Dusk', 'Teal Seal' or 'Coil of Void' in the original language. Those uber spell were also built much like Astra weapons of mass destruction in Hindu mythology, and as gods directly wielded those, they could only be countered by similar level spells, and only if said spell belonged to a god of similar or higher rank.
5) Death had stages, called Circles of Sansara/Samsara and each character had three right on character sheet: first one was a normal character, once dead was a sort of necro-being with strong affinity to necromagic and some vulnerabilities in addition to their normal abilities, and twice dead was a ghost with its own abilities entirely (this reminds me of Hollowing in 'Dark Souls' a bit). 'Raise Dead' only moved the target one Circle higher, and a lot of mages preferred to keep the spell to themselves, especially in early ages when it was X/life casting. Those who were agree to cast it on some travelling vagabounds such as our characters, usually demanded something very important in return, usually under an oath of True Name (which we also had).
6) Alchemy, astrology, witcher Signs and so on had their own subsystems grounded in actual alchemy, astrology and mudras/mantras, which gave lesser effects but which were free for PCs to mess with, and better defined; sadly I never played any of those classes and don't recall those systems in any details, but I recall that when we had an alchemist or a witcher in a group they salvaged almost everything they could get their hands on 'for materials' and later something blew up to various effects.
7) I don't recall any priests or paladins as classes, or, at least they weren't played often because mages healed too and gods were mostly either alien due to enlightenment or arrogant jerks; sometimes those two qualities were combined. Light side was just as much jerks as Dark side only more pretentious and with better PR. Feralard, tellingly, didn't have any acting, influencing gods - they either sealed themselves off to Valinor, achieved full enlightenment or died off in previous cataclysms.
8) It was a legacy of board game, I think, but monsters were rarely outright aggressive. The board game had aggression table - basically the a random initial mood of an encounter, from sleepy to murderous, with most reactions falling in the range of 'variously interested/indifferent/mean to adventurers', but even predefined dungeon encounters usually had an option to bribe or plead your way out. XP for monster murder or for gold gathered was a very small factor (due to the process of the game itself, below) so you could bribe, negotiate, trade, plead, sweet-talk, make laugh, bring to tears, bluff, intimidate, mislead, fool, hire and sympathize with almost everything, even a monster who looked like a flying arse and behaved almost as such. I recall making a Nazgul extremely depressed with song of my own actual writing about how much of ungrateful job a being of Nazgul was. You could make a blambia (kind of multicoloured mist of mutating properties) to shy away from lewd poems, hire monsters to do your bidding and so on.
There was rather a lot of poetry going around a table. Bards were given a permission to sort of use any kind of song or poems if players could read them from memory but the general feel I remember that any kind of poetry always worked to some beneficial effect if you made it yourself right in the game, preferably on fly, even if it was a simple rhyming verse or abovementioned lewd poem.
9) With all his talent for careful wordbuilding and passion for subsystems the DM's style of play was almost mad libs random, a pure improvisation. I think he was most interesting to see what we are going to do with each encounter or an aspect of the world than to aim for any actual adventuring goal. It was never boring but sometimes frustrating game, and you could have started on a road being killed by bandits only to go after One Ring thirty minutes later; sometimes several levels were gained and lost (or traded off) in each session, sometimes as much as ten, so XP was rare a prerequisite to vagabond wanderings.
But if you managed to get at least thirteen levels due to actual progression as scant as it was and not because Sauron had a bad/good day, you could retire your character and your PC then became a part of history of the world, with his own tower, castle or city actually painted on a map. You could design this tower/dungeon/city and more often than not even meet your previous reincarnation in later play.
There was no prerequisite for PCs to stay in a group either. We usually started in the same place but were free to go and mess with world on our own, explore, made agreements and get into troubles as we wished. It made the game basically running solo threads for 3-4 people, with DM taking turns or more experienced friends of his being assistant DMs for other players. If you needed, say, to take time to write depressing Nazgul song or to make a clever plan, or to draw a fake treasure map you were going to give a cobold* with aims on your kidneys, it was very much ok to take the time and do so. I don't know if it was because of this style or due to some other factors but there was not a single instance of PK or some such betrayal in any of games I've played.
* (who was cobold because we knew of Cobol more than of actual kobolds)
10) Dungeons were permanent (within age) landmarks and mostly legacies of the board game, used as a setup to future troubles and plot hooks more than a place to get gold or have a logical purpose. Each has a theme, some lore, a general level of a danger (Tower of Bjornir the Bear was more troubles than Tower of Furdis the Mage) but none was very sensible overall - in one room you could meet Saint Aubeck in disguise selling prophetic cookies with aim to conscript people to fetch the Holy Grail, next room it could be blambia seeking to wed a princess and the next room could have been a Nazgul asking for some ridiculous toll fees to cross a bridge because he had a day off and was bored*.
(we didn't know about Monty Python but that encounter sometimes played kind of similar and sometimes very much not).
11) Combat was the blandest part - basically DM took the core from whatever mechanical system he got the latest, tossed away everything that didn't fit and added mechanics for classes such as witchers or dragonriders so they would work more or less like their cool literary prototypes. Last time I played the game used heavily reworked 'Skills and Powers'. You hit things, they mostly stayed hit. Unless they are Saint Aubeck in disguise. Or blambia. Or Nazgul on his day off. Playing a fighter was mostly short-lived career and on my own I never got higher than level five but it quite fun nevertheless.
12) Metagaming and out of game distractions were dealt in-game with a flying squad of sixteen Scottish vampires. Somehow it was always both hilarious and scarier than Sauron.
13) As anything but 1d6 die was not even a concept, much less a stuff you could buy, the main dice mechanic was '1d18' = 1d3 + 1d6 where 1d3 defined the range of what d6 shown: 1-6, 7-12 or 13-18. Sometimes dice were added together to form 3-18 roll and some other variations of d6 rolls were also used. Rolls were mostly under the stat, but also over the stat, on not a directly related stat, on luck, under or over gold/level/current phase of a dominant moon (if you played an astrologer) and so on. There was probably a stricter system on which roll was for what thing but as the only printing method we had was a Ephraim's typewriter, the system itself wasn't much described, only applications of it, which for me looked pretty chaotic.
14) Even before more RPG information became available we got away from 'class+race combined' approach as it didn't let us play what we wanted to play.
15) AC from armour was generated through a formula A*B+C.
(A was an 0.1-0.6 zone coefficient what approximated how much of vulnerable body area the armour had covered. All zones added up to 1, with 0.1 given to least important stuff such as gloves and sabatons and 0.6 for chest/abdomen; B was a material coefficient, ranging from 1 for leather and ending as high as 10 for mithril and other special materials, and C was a construction coefficient, for scale/chain/plate and so on, ranging, AFAIR, from 1 to 5).
While it was quite time-consuming to calculate all those armours without any computers, and in a long run unnecessary for the system that didn't have by-zone targeting and HPs, it lent itself very well for piecemeal armour.
This is mostly all. I don't know if Ephraim even remembers those days or his strange world, but I still 'borrow' from it all the time, although in approaches (such as not very aggressive monsters) more than details.