Hierarchical Cluster Engine is a a solution that can be used to construct custom network meshes or distributed network cluster structures with several types of relations between nodes. It supports handling of management requests from multiple source points, native reduction of results from multiple nodes (aggregation, duplicate elimination, sorting, etc.), a powerful full-text search engine and data storage, transaction-less and transactional request processing, and many language bindings for client-side integration.
libktomgirl is a library that reads a subset of the Tomboy file format. When it's done, it should support reading and writing all aspects of files created by Tomboy, Gnote, and KTomGirl. Despite the K in its name, there are no KDE or Qt dependencies (nor C#, GKT, or GLIB). This is pure C++ with boost and stdlib only. Most of the code is from Gnote.