Hi,
I'm developing a 4 dimensional tetris game called 4dtris. It has a different concept than the other 4D tetrises I know (Frac4D, Hypertetris, Polytope Tetris). It uses double perspective projection to visualize 4D instead of sub-views. I would be glad to hear some opinion, suggestion about it.
Project page and downloads: https://launchpad.net/4dtris
A trailer video: http://www.youtube.com/watch?v=dmWRtz97lfU
It's open source, so if you are interested in the code, you can browse it in the project site.