Not entirely sure how functional it is, but Planeshift has been around for a very long time (they started well before WoW or EQ2 release). For a long time there was a small group of people barely making any progress with it, but in recent years they've been picking up in development.
Other than that look for games developed with Ogre3D, OpenTK, SlimDX, XNA, Crystal Space, and Irrlicht. Those are APIs that are all freely available to download and start working with tailored toward game development. Any indie game developer worth their weight will have heard of a couple of those and likely have tried them as well. XNA is perhaps one to be weary of, while it's a fine API, being a Microsoft product which opens up Xbox360 and Windows Phone 7 development it tends to attract a lot of lazy people that have no end of excuses on why they wont study the documentation but will actively copy paste code snippets they barely understand.