python is a Python binding that directly glues to a state tracker. I don't like it much; I'm sorely tempted to write my own.
wgl and egl are other windowing system trackers similar to dri; wgl is for Windows and egl is an implementation of the EGL standard.
g3dvl is the old video decoder Younes wrote for GSoC a few years ago. The Gallium API's changed and it's rotted a bit so there's ongoing work to refactor it into the rest of the codebase.