I just played my first Rules Cyclopedia based game

[AdmundfortGeographer]

If your gung-ho about it, check out some of the Gazetteer line for Mystara; they introduced some new classes and race-classes as well.

Also introduces more spells and skills.

Classes introduced:

GAZ 1: Nothing, just the best Points of Light setting, evar, IMO.
GAZ 2: Desert Druids, unique spell list for a cultural subset of druids.
GAZ 3: Seven Secret Crafts of Glantri, Alchemy, Dracology, Elementalists, Illusionists, Necromancy, Cryptomancy, Witchcraft. [Something of arcane specialization]
GAZ 4: Nothing
GAZ 5: Elven Magic-User class [Effectively, the first prestige class. Spell list is a mix of clerical and arcane]
GAZ 6: Dwarf Cleric class
GAZ 7: Clerical rune magic
GAZ 8: Halfling Master class
GAZ 9: Merchant-Prince class (a ship captain)
GAZ 10: Wiccas and Shamans (monstrous clerics and magic-users), Kobold, Gobling, Orc, Hobgoblin, Gnoll, Bugbear, Ogre, and Troll characters.
GAZ 11: Merchant class.
GAZ 12: Shaman class (named the same as the class for monster characters, but this class is more like a 3e Spirit Shaman, humans only)
GAZ 13: Shadow Elf class and Shadow Elf Shaman class. [Shadow Elf Shaman is yet a third type of shaman.
GAZ 14: Shamani class. [Yup a 4th shaman-type class]
Dawn of the Emperors: Forester class and Rake class [Forester is a human fighter/magic-user, Rake is a thief without Pick Pockets and Backstabbing]

PC1: Treant, Wooddrake, Centaurs, Pooka, Pixies, Fauns, Dryads, Brownie, Wood Imp, Sprite, Leprechaun, Hsiao, and Sidhe character classes.

PC2: Aquatic Elf, Kna, Kopru, Merrow, Nixie, Sea Giant, Shark-kin, Triton character classes.

PC3: Faenare, Gnome, Gremlin, Harpy, Nagpa, Pegataur, Sphinx, and Tabi character classes

PC4: Devil Swine, Werebat, Werebear, Wereboar, Werefox, Wererat, Wereseal, Wereshark, Weretiger, and Werewolf character classes

Hollow World: Introduces the Wokani and Shaman classes from GAZ 10 as PC classes.

 

[Remathilis]

PC4: Devil Swine, Werebat, Werebear, Wereboar, Werefox, Wererat, Wereseal, Wereshark, Weretiger, and Werewolf character classes

OMG I Played that! Fun for a while let me say, but ultimately ended like a bad Werewolf: The Apocalypse game; PCs tearing at each others throats. YMMV.