WhatsApp protocol implementation for libpurple (pidgin)
BlankOn users can use suroboyo repository
Windows users can find a copy at the nightly builds server: http://davidgf.net/nightly/whatsapp-purple/win32/
Just do make (if you have to choose 32/64 bit, run make -f Makefile32 and pick the proper makefile).
Makefile.mingw is the makefile for Windows 32 bit.
Check http://davidgf.net/nightly/whatsapp-purple/ for nightly builds ;)