We used QT mainly because our team was kinda gathered from leftovers (we didn't know eachother before) and had an OS problem - we had two computers with Linux, two with 64b-Windows7 and one with WindowsXP, so we had to use something that was portable. Qt was proposed by one of the guys; we all agreed, as it is quite a big framework and offers a lot of features.

All gfx is done in OpenGL; I don't know it (that was also one of the reasons I didn't really have much to do... Gotta try learning after the exam session), so I can't really tell much. I think they are either shaded circles or circular sprites (with alpha decreasing from the center). As for their behaviour, all physics is done by the Chipmunk lib - in case of lava, it's simply a lot (1k when project begun, later reduced to 700-800 to combat lag) of equal-radius balls. If you were really curious, I think there is a .zip with sources attached.