Fidelio is a hotline client for GNU/Linux, that uses Gnome and Gtk+. Fidelio presently has the following functionality: Server and Tracker Bookmarks, Tracker support, Multiple simultaneous connections to different servers, Userlist and messages, and more.
(shareware) GHX is a clone of a mac software gathering in one program FTP, IRC and NEWS like functions using a proprietary protocol.
GtkHx is a GTK+ Hotline Client based on Hx.
Opensprings is the home of open source projects based on Hotline technology. The main project is OpenSprings Modules a comprehensive, cross-platform, open source set of C++ development libraries.