Swiss company Synthesis AG has released it's SyncML Client library (libsynthesis) as open source under the LGPL v2 and v3. The software is already used as the foundation for commercial synchronisation solutions for Windows Mobile, Palm OS and the iPhone OS and is also used by the Moblin project in the SyncEvolution v0.9 synchronisation tool. More details can be found on the libsynthesis page on Synthesis AG's website.
SyncML (Synchronization Markup Language) is a system of platform-independent standards for synchronisation of PIM data between mobile devices and servers. These standards are maintained by the Open Mobile Alliance (OMA).