[rw_grim]

You could just use libpurple to do all the im stuff and literally just write a user interface. That said, purple 2 isn't really designed for modern chat networks, but we're trying to solve that with the still unreleased purple3.

You may be interested in our State of the Birds which cover libpurple and pidgin development. https://discourse.imfreedom.org/tag/state-of-the-bird