Play a DS against PSP on Tic Tac Toe!
Flagon has released his project Net Tic Tac Toe for both PSP and DS. I bet you know what Tic Tac Toe is, so I won't have to explain anything about the gameplay. However, this homebrew lets you play between a PSP and a DS. Currently the IP address is hard-coded into the source, so you can only launch it on two handhelds and wait for them to establish a game.
Download the PSP version
here.
Download the DS version
here.
Download the source code
here.
Source:
Flagon's Home Page