Jangle (Just Another Next Generation Library Environment) is an Open Source project to provide API access to library systems. They are following the the DLF ILS Basic Discovery Technical Recommendation. The DLF Technical Recommendation is the end product of the "Berkeley Accord", where most major ILS vendors agreed to support a set of essential functions through open protocols and technologies by deploying specific recommended standards to harvest data, query available information and permit the creation of stable links. Jangle = middleware for an interface between ILS and external applications.
A more complete description of Jangle is posted on the Dillettante's Ball here and here. It's an ambitious and even audacious attempt. It could change the way librarians interact with their ILS vendors and customers. If you have the skills, Atom Publishing Protocol and "use, manage or just want simple access to a library system" they welcome your participation.
More about Jangle at jangle.org and Google groups. Slides from a lightning talk on Jangle available here.