What is some of your favorite Open Source software?

http://online.wsj.com/community/groups/linux-unix-bsd---free-open-691/topics/some-your-favorite-open-source?commentid=1626016
Wall Street Journal: Linux, Unix, BSD - Free and Open Source Software

Some of my personal favorites are:

GIMP, Inkscape, Blender (Graphics),

Firefox, Apache, Skype, Pidgin, Xchat (Internet),

OpenOffice, Scribus, Lyx (Office),

Xtuple Postbooks ERP, OpenBravo POS (Accounting),

Audacity, Avidemux, VLC, Mplayer, K3b, AcetoneISO (Multimedia),

MySQL, PostgreSQL (Database),

Bluefish, QT, GCC Compiler, C/C++ (Programming),

MamepGUI (Gaming).

There is so much more.