I am currently working on OCaml-bindings for the Last.fm public API. The API provided by Last.fm allows access to most of the data hosted by their service, such as listening data, artist info, tagging-data etc. The bindings are hosted at OCamlForge a public hosting site for Open OCaml Projects. You can find all info for the library here.
There also is another project that works on the API for OCaml. However both librarys cover different parts of the API. The one I am writing allows access to all the API parts that deal with data querying while the other one allows scrobbling and listening to radio.