Earlier this year, unnoticed by us here at Rampancy (fancy that) the long-standing disputes over the ownership of the source code for the popular Hotline chat and pira.... err, file-sharing client and server seem to have come to an interesting conclusion, with the open-sourcing of the code for Hotline 1.x and the publication of the protocol specifications. The new project has been renamed OpenSprings. Apparently the code is available either under GPL or a commercial license. The commercial version of the app is still being maintained by HotSprings, Inc., which apparently now owns the code.
Personally, we at Rampancy are still using the very excellent FrogBlast clone for OS X, having abandoned the official Hotline application after it was no longer possible to close or hide the ad-banner-bearing toolbar. However, if you're game to give it a try, you can download the newest version, 1.9, of the official client and server from the Hotsprings, Inc. download page. Versions are available for OS X, Mac OS Classic , and Windows.
Incidentally, Rampancy still operates its own Hotline...err, HXD server, at hotline://rampancy.net.