Seb Lee-Delisle made this cool particle system using an Arduino board and an 8×8 LED array. He writes:

The only real trick here is that I’m working internally with a much higher resolution that the actual 8×8 grid, and then rounding to the nearest pixel when displaying each particle. This gives a really smooth movement. I’m only actually lighting one LED per particle but due to the Persistence of Vision (POV) effect it looks like there are more.

Source code included!