Arcana Unearthed, later Arcana Evolved, was Monte Cook's formal dissent from the "3.5" edition of Dungeons & Dragons. It features several new races, classes, feats, and theory-of-magic. The first book was billed as an alternate Players Handbook but the revamp peed all over that, by incorporating setting-specific information (see below).
Several of the AU features parallel points of Stephen R Donaldson's Thomas Covenant series, especially the first one. The Giants who travelled here by ship from the east, and now cannot get back home? Oh yeah. The weaponless fighter who powers himself by the sheer force of his oaths? That's the Oathsworn. Also the emphasis on ritual over one-shot melee spellcasting.
Like Talislanta, this setting prides itself on lacking elves and promptly dumps the next best thing here, namely the faen. Other races include dogmen and catmen, here the Sibeccai and the Litorians. The Verrik are emo humans. And finally there's the Mojh, ultimate dragon weeaboos. These "scions" were human once and have undergone a ritual to be lizardlike (faen have body dysmorphia too - they become sprytes).
The Diamond Throne
Alignments are NOT part of this text. Look at you, "with us or against us". What are you, some kind of George W Bush voter?! (These books were a Product Of Their Time, as the saying goes.)
Errr... alignment is sort of not part of AU. The AU tweaks were playtested in a special setting, Diamond Throne. Good and evil couldn't quite be glided over.
DT makes clear that there did once used to be such a thing as eeevil. Lord Foul was played by the dramojh, something like "our scions" in Draconic. Some asshole dragons got into their scaly horny heads to juggle some demon-testes called Tenebrian Seeds. Thereby were spawned these nightmarish mixes of man, dragon, and spider (because creepy) who subsequently took over THE WORLD, at least the northeast side of their continent.
After centuries of tyranny and body-horror throughout this book's map, the Giants got loose from Donaldson's book and anchored off the coast. The liberated humans sided with them; the lore is less clear on the Litorians, who might have rebelled by themselves first, but they too rallied to the giant-human alliance. Subsequently ensued a war to the knife, eradicating the dramojh, much to everyone's surprise. The humans soon found themselves under new management - Giant management. Suckers!
Diamond Throne accumulated a few extra splatbooks: Legacy of the Dragons for some NPCs and new-ish monsters; Mystic Secrets for power-rituals, runes, and settings. Also the minor publishers Fiery Dragon and Mystic Eye offered some adventures around Ebonring Keep, nigh on the Floating Forest between the two north/south mountain-ranges.
These supplements offer additional sentient races. The Alabast are alien Noldor from elsewhere (but they're Not Elves because shut up). The Chorrim are militaristic hostile humanoids from the caves but aren't orcs or hobgoblins because get bent. The Rhodin (who live in Ptolus too) are scavenging thieving humanoid scum but aren't goblins because fuck you.
The whole AU / DT universe never was as original as it wanted to be.
Oh, and there was a short-story collection, something about "rune children". Runes were a theme in the AU / DT universe. A big theme.
Here's where this sequence and this setting jumped the shark. Start with the colour-theme, which AU had as a nice eye-pleasing yellow-on-black formerly and in AE is an eye-blasting white-on-red.
Everyone was just figuring out how the AU / DT world with its overhauled d20 system was going to work and OH HI WE'RE THE DRAGONS AND WE'RE BACK NOW. We didn't even get a gazetteer of a single starter location.
So, here come the Dracha, dragon-men. And the dragons come behind them, bearing gifts... Tenebrian Seeds. Some races can use these to become Evolved or Transcendent or whatevs; giants become taller for instance. Because nobody ever listens to the historians. And we thought Cook was writing fantasy...
This is perhaps the Malhavoc Press answer to Dragonlance. Takhisis doesn't come to conquer; she comes to seduce.
Anyway, the massive AE book makes a Dragon-sized blunder in bundling the player material with the DM, guaranteeing that the DM is going to make some awful decisions in how to parcel the former to the players - handing a PDF excerpt to them, most likely.
This version at least had a first-party adventure-module. Mike Mearls, Ruins of Intrigue. The ruin (singular) is an arena, between dragon and giant. The ruin was once a dramojh nursery; the giants and dragons are working out who gets the loot. Mearls tries ever so hard not to take sides, because a major theme in this universe is that alignment is Nuanced, but... only one side can make new dramojh, and that's the dragon side. Did anyone even play this thing who wasn't playtesting it?
Nobody's done much with the AU/AE rules, nor with the Diamond Throne setting, in some time.
It was full to bursting with ideas. And it's not like you HAVE to play a morally-ambiguous campaign; there are plenty of baddies left post-dramojh, especially in the mountains' underdark. D&D parties were doing just great thumping goblins in B2's Caves of Chaos, or managing diplomacy or even running a kingdom in the Companion set.
What killed this setting was the dragons. Whatever the party does, in the back of their heads they have to know it won't matter here, because they don't matter here anymore.