Tenebrae was already compared to several things – Black Sun, and Dying Earth, and BLAME! (and I expect 'Veins of the Earth' and 'Into the Odd' to be mentioned at some point) – but where Black Sun is aggressive, inescapable despair, and Dying Earth is baroque cynical adventureland, and Blame is endless, mostly desolated, city, the Dungeon in Tenebrae stands on its own being none of these things. It is more hopeful than Black Sun, it is already in dead world, (so not really _Dying_ Earth), and, unlike in Blame!, instead of the city it is the literal underworld sewn with dead memories of the world's better and louder times made flesh. Whatever remained of the Last Empire clings to life in pocket stronghold(s) between the surface (that is grabbed by Void in an attempt to devour it) and the Dungeon of the afterlife (which patiently waits for the surface to let go, be devoured and pass on, probably resetting the world), and where living cannot travel without aging to a dust in about a minute. All those gnolls, and goblins, and beholders that PCs meet in the Dungeon are, from what I understand, already dead, and appear because the underworld relives the memories of its past when Masks and/or living people trigger those memories when they venture through.
Masks are the most unique mechanic in Tenebrae, because in order to travel through the Dungeon ritualists-adventurers wear the mystical Masks of various mythical archetypes, Hero-of-Thousand-Faces style: the Dungeon and its dwellers see them existing as their Mask's archetype. Right now there are only four Masks (Zealot, Untamed, Arcanist and Knave) but at least one more non-PC mask is mentioned, and rules for swapping Masks are also here; I immediately wanted to add a sort of Jester or Sage masks, maybe combining them both into Madman. PC's identity in the Dungeon is not important: it isn't the PC that has HD, better AC and extra vitality able to withstand the underworld, it is the Mask. It isn't PC that levels up, it is the Mask. It isn't PC that gets all those powers, it is the Mask, and Masks can be swapped, and found, and, presumably, lost or ripped off, which, at the very least, is interesting because it makes PCs so vulnerable.
The second most unusual thing is how Tenebrae handles gold. With sun, and moon, and stars devoured by the Void and officially out, gold coins in this setting are mystical nodes of power, light and essence, encapsulated by Last Empire. While coins themselves are presumably very long-lasting as essence sources, they are exhaustible, and what remained of living world is powered exclusively by them: PCs travel into the Dungeon to get gold, but for survival, not a luxury, and not even their own personal survival but of their whole settlement and probably all of the living people. In the current document the aspect of PCs' obligations to their home Stronghold isn't touched upon but I can imagine that at least some of the initial gold has to be given away for PCs to have a place to return to from their travels. It is possible that PC ritualists are the last hope of their home, but in the absence of other information, the survival of the home Stronghold can be played as harsh or soft as DM wants it.
To have a safe spaces PCs, in downtime, will have to create their own or extend their home Stronghold. Unlike in most of the games, where castle-buildling feels kind of tacked on so high-level characters had something to do to feel important, in Tenebrae you cannot even level up (your Mask) without building an appropriate shrine, which I think is very interesting, twice-indirect way to deal with XP-for-gold idea. The document gives a few examples of the what can be built but it can be expanded upon, and I hope it will be.
There is a simple system in the document that is comparable to systems such as 'Into the Odd', 'Black Hack' or 'Knave'; if you favour another system, it can be easily translated. By my estimation the original system for Tenebrae is quite deadly, despite PCs having renewable Insight pool which they can spend to slightly sway their chances for the better. Stats are given equal importance, which I like for this setting, because however the character rolls they will probably be lacking in something, be it Wisdom (that affects AC), or Charisma (for saves), or Dexterity (for to-hit); PCs here are definitely not super-heroes-good-at-everything even with the Masks. At least initially, PCs are aggressively limited on how much of useful stuff they can carry (this is when Tenebrae reminds me of 'Veins of the Earth') but, as there is no armour beside what the Mask gives you, it is more manageable than it looks like. Gold is measured in the same Slots as everything else, so encumbrance indirectly is also the currency system. I am finding the description on Bow to be strangely detailed and when I read it for the first time, I misread it so 'Bow' looked like it describes any projectile weapon; I guess it can be very easily reskinned to be like gun or like a gun that Stronghold People call 'a bow'.
One of the little strange things about Tenebrae is, as by the wording, the living rutialists don't have to eat or sleep to survive in the Dungeon. Rations are ritualistic meal needed for camping and restoration but aside of that, from worldbuildling point of view, people don't starve or fatigue in the Dungeon. I am finding this little detail quite unique. Is it because there is no time, in traditional understanding, in the Dungeon? Is this because of the Masks who made a living being more of the archetype than a purely flesh and bone entity? It is because PCs kind of die a bit when go to the literal underworld to fight various memories of various ages?
Camping is a main unit of time within the Dungeon. Without need to eat or sleep for survival, and no sun, and the Dungeon being the underworld where memories of different ages mix and meld, it is a good way to keep track of time. From what I understand, there is no way to get more rations in the underworld of Dungeon (undead things don't sustain the living, and eating twice-dead-memory-denizens is, probably, not an option) so when getting their gear PCs already know for how many 'days' they can travel, and the loss of even one ration can be disastrous. A lot of the aspect powers also work 'until next camp'. It is a good system for this setting and ritual-survival mood.
Aspects of Masks is another idea that I really like. It is ten 'spells' for each Aspect that emphases the Mask archetype, be it 'Rage' for Untamed, or 'Sneak Attack' for Knave, or 'Fly' for Arcanist. In the beginning PC chooses one Aspect and rolls for the second randomly (which, sentimentally, reminds me of Synergon RPG and its semi-random starting Skills), and can evoke either one of these Aspect once until next camp. With each new 'level' the Mask gets, it awakes one more random Aspect and gets one more time to evoke any known Aspects, in any combination and order. Comparatively to regular spells Aspects are somewhat stronger and I especially like how
There is one named NPC and several other creatures, but Denizens section hopefully will be expanded. As of now, Barberians look a bit out of place but I think it is because there is not much else to compare them with. I really want to see Locales too as I wonder how the Dungeon will be organized, given that it is either endless or extremely, extremely huge. Will it be 'procedurally generated', symbolically built, built like an actual dungeon, something else or everything at once? Giving the scale and the nature of the Dungeon I think there will be at least some fluidity in the structure, but, on the other hand, Underworld of Exalted had a map, and cities, and quite stable environments, so I am curious to see how it is for Tenebrae.
The writing is very terse and gripping at the start but grows somewhat loquacious later; this being a work in progress I am ok with it because if the latter pages at any point in a future get to be as good as the first ones, it will be enough. One little thing that struck me as odd is how in 'Adventuring Rules' section words 'narrative resolution' are used. To me 'narrative resolution' by default perception meant some kind of story-driven-game, where the result of the scene is what fits the bigger agreed-upon story or theme (and not the logic of the setting, the situation or the environment), but these words here are used to describe, basically, 'make PC say how and where they search, give results based on this and don't solve the search with dice rolls', which I found to be unusual way to speak about it. Probably necessary wording if people playing the game come from something like Pathfinder where you roll for pretty much everything.
All and all I really want to see Tenebrae finished. There are a lot of potential and very strong setting/mechanic aesthetics here.