libfolks is a library that aggregates people from multiple sources (eg, Telepathy connection managers for IM contacts, Evolution Data Server for local contacts, etc.) to create metacontacts. It's written in Vala, which generates C code when compiled.
libfolks' Vala API is stable (in the 0.6 series onwards), but its C API may vary depending on which Vala version, GIR and bindings versions and libgee version it was compiled against. We guarantee Vala API stability until we announce breaks, but unfortunately cannot guarantee C API/ABI stability because of the nature of Vala.
Folks developers can be found in #contacts on irc.gnome.org. Folks' mailing list is firstname.lastname@example.org, for discussion of the development of folks itself as well as applications using folks.
Bugs can be filed in the issue tracker.
See the roadmap page.