Hey, even though we're getting familiar with 3dgs and for some things, it's a great engine, we're looking for one that is cross platform (Windows, Linux, and if possible Mac) for our next game.

We've looked at a few, (Ogre, for example) but most of the ones we've seen are either only windows, or unpayable for indies or else they're specific to one type of game, which we don't want.

Some things that it should feature
-classes (if possible not just structs, but actual classes)
-multiplayer
-Shaders
-possibly a good entity system (heirachical? not a must)

Has anyone seen/used good cross platform engines? Wikipedia's list of game engines doesn't really satisfy me...