The CoreLibrary is a multiplatform object library for C++ (Linux, Win32, MacOSX, PocketPC).
It provides many of the common objects found in Java (Strings, Threads, Collections, etc.) and has the ability to send objects across the network like CORBA.
Symwire is a Host-based Intrusion Detection System (HIDS) and Integrity Checker written entirely in open c for symbian. It aims to be a complete, free, multiplatform, and open-source solution for detecting modifications and tamperings in files.