Last Updated August 14, 2016.
Fldigi, a digital modem program for Linux, Free-BSD, Mac OS X, and Microsoft Windows XP, W2K, and Vista. Supports modes CW, Domino, Hell, MFSK, MT=63, PSK, OLIVIA, RTTY, Thor, and Throb.
WSJT-X weak signal software from Joe Taylor, K1JT. This software supports WSPR, JT-65, JT9, and other MF/HF/VHF/UHF modes. Open source with GPL license, and uses the Qt multi-platform GUI kit. Source code can be compiled for Windows, Linux, FreeBSD, Macintosh OS X, and most other UNIX-like operating systems; binary installation packages available for Windows and some Linux variants. I have no problem compiling these for Fedora Core Linux.
VOACAP Online. Web site based on VOACAP, but with new "frequency-time wheel" presentation in addition to coverage maps. Also handles direct or long path predictions.
Gpredict. A real-time satellite tracking and orbit prediction application. Integrates with hamlib to control radios and point antennas.
GRIG. Simple ham radio control program based on Hamlib. Integrates with other Hamlib logging and digital modes applications.
SDR-J - Jan van Katwijk's multi-platform (Qt toolkit) SDR software for SDRPlay and many others...
HDSDR - Formerly called Winrad. Nice SDR software, works well with CWSL, HDSDR, and Fldigi. Windows only
CWSL - CW Skimmer Listener - Great utility that "breaks out" the up to 7 QS1R CW Skimmer Server channels so that you can process them via HDSDR and other digital decoding software. From Peter, OK1FFU via OL5Q Club. WIndows only.
Virtual Audio Cable by Eugene Muzychenko. Commercial, WIndows only
Ngspice mixed-level circuit simulator, multi-platform. Update - release 24, 2012-01-31.
gplEDA GPL's suite of Electronic Design Automation tools. gEDA has been selected as a Google Summer of Code 2008 project!
GAEL -- GNOME Assisted Electronics. The successor and assign of Oregano....