libninjam is a set of development libraries for creating custom NINJAM clients, compatible with standard NINJAM servers, and for extending the NINJAM protocol with new features. NINJAM clients and servers using this library, ensure compatibility with the conventional NINJAM ecosystem and gain new features, merely by upgrading the library. Through collaboration among the various NINJAM software developers, this allows the NINJAM community to advance the state of the art, without imposing compatibility conflicts upon users, and reducing the over-all work-load of developers.