Races of Destiny: Chameleon
It, literally, can be a Fighter, Cleric, Wizard, Rogue ... Barbarian, Fighter/Wizard, Mystic Theurge ...
Basically in the morning you get to choose 1-2 ability sets for the day, choosing from a pretty wide range, and get abilities similar to (but not as good as) the various core classes ... then you can mix and match them later, and switch them out during the course of the day once or twice. You also get a feat that you can change out every morning and a +2 ability score bonus you can change out every morning.
Sounds like a blast to play. I doubt it would be overpowered, since it doesn't "max out" anything, but it would be interesting to be able to do just about ANYTHING when the need arose.
--fje