GameWrite
GameWrite is a miniature IDE that can be used to create Pocket PC games and multimedia applications on your Pocket PC using VBScript. It's possible to do this without using Embedded Visual Basic or a desktop compiler. GameWrite uses the ASpriteCE Game Control as it's engine, and you can access any of ASpriteCE's functions from within the IDE.

Sync4j
Open source SyncML based mobile application development platform. It includes a SyncML server, SyncML API to build disconnected mobile applications, SyncML clients for Outlook, Pocket PC and BlackBerry, a connector to Microsoft Exchange.