GridWars 2 is a Geometry Wars clone. The player gets points by shooting at anything that moves all with psychedelic an flashing graphics.
The gameplay of Grid Wars 2 is crazy. But it is hard to figure it through static images.
For example: http://www.youtube.com/watch?v=oMboEDWm8DQ
Vivid, fun and works on my 3 year old laptop.