Metakit is an efficient database library with a small footprint. It's a cross between flat-file, RDBMS, and OODBMS.
Keywords: structured storage, transacted, load on-demand, portable, C++, Python, Tcl, instant schema versioning.
Xapian is a Search Engine Library, written in C++ with bindings for Perl, Python, PHP, Java, Tcl, C# and Ruby. Xapian allows you to easily add advanced indexing and search facilities to your applications. See www.xapian.org for more information.
Powerful platform for creating networked multiplayer 3D games. The system includes specifications for a client engine and 2 protocols. Demo apps: mud/moo proxy, tetris. Currently uses OpenGL, VRML, java, tcl. Client/server architecture for security.