Cool software

There is so much excellent software available under the various FLOSS licences, so please add your favourites here:

Rosegarden, this is free music software including audio and MIDI sequencing, score editing and a general-purpose music composition and editing environment. "...the closest native equivalent to Cubase® for Linux..." according to Sound on Sound. The same company sell a product called "Studio to Go..." a Live CD with Rosegarden. This means that you can carry the CD and your USB memory device and use any computer as a specialist music PC. (GNU/Linux only)
OpenOffice now includes a database with wizards. It is one of the best productivity software suites available - with easily the best price tag. (Multiple OSs)
Firefox is a great web browser, with tabbed browsing and many privacy and security features. (Multiple OSs)
Dia is a drawing program. It can be used to draw many different kinds of diagrams. It currently has special objects to help draw entity relationship diagrams, UML diagrams, flowcharts, network diagrams, and simple circuits - and you can add your own. (Multiple OSs - see http://dia-installer.sourceforge.net/ for a Microsoft Windows version.)
7-zip is a program for creating or unpacking archived and compressed files. It can unpack 7zip, ZIP, CAB, RAR, ARJ, GZIP, BZIP2, TAR, CPIO, RPM and DEB files, or create file archives in those formats.

The OpenEducationDisc project and its parent project the OpenDisc are well worth a visit.