SharkTorrent is an open source C++ BitTorrent client for all platforms supporting c++, libtorrent, WxWidgets and boost library. That is at least Windows 9x, 2000, XP most Linux/Unix OS-es and Mac OS. So far, SharkTorrent has only been compiled and tested on Windows XP, Debian Linux 4.0 and Wine with Debian.
Download: SharkTorrent 0.1.4 Beta
May be the next uTorrent?