ghpsdr is a software defined radio client written specifically for HPSDR by John Melton. It uses a modifed version of DttSP that is ported from the Windows version. DttSP is built as a static library that is linked with the GUI code.
The software is being developed on the Ubuntu version of Linux (specifically version 9.04).
Currently (early August) it does not have a transmit function, but that is expected shortly.
The software is available from SVN at: svn://220.127.116.11/svn/repos_sdr_hpsdr/trunk/N6LYT/ghpsdr (How to use SVN) and includes a precompiled executable in the bin directory. The README explains how to compile the source for a 64 bit system or if you wish to modify the code.