ChessNET, one of 25 other entries in the NDS/GBA division of Neoflash's Spring Coding Contest, is an online chess game with an interesting feature that we've yet to see in any other online-enabled DS games -- play-by-mail-style matches. Every action is saved onto an online server, so you don't have to stay glued to your handheld all night. After your opponent moves a piece, you can wait hours or even days to deliberate over your response. Likewise, your opponent can play other games or turn their DS off while waiting for your next move.
A play-by-mail option like this would have been perfect for Advance Wars: Days of Ruin and many other turn-based titles with plenty of inactive stretches. Sony Online Entertainment certainly agreed, as the developer implemented it in its Advance Wars knock-off for the PSP, Field Commander. Nintendo even neglected to provide the feature in Wii Chess, a seemingly obvious oversight.
CYBER_Aeon, the programmer behind ChessNET, has plans for more features that should come standard with almost every online-enabled commercial game -- messaging, buddy lists, and account handles.