I have not tried all of these (yet)

Quisk
http://james.ahlstrom.name/quisk/

SDR Shell
http://code.google.com/p/sdr-shell/

Lysdr
http://lovesthepython.org/git/?p=lysdr.git

Quisk worked with Softrock Ensemble RXTX with only a few minutes of setup. I will try the others once the kit is finished and back a point where I can hook it again.

73 de NG0R