Although open source has its origin in the UNIX/Linux world, quite a lot of open source applications are available for Windows as well. I'll provide links to a few lists where you can pick up useful and interesting open source programs:
- Google Pack - A good collection of open source Windows apps - Packed by Google
- WinLibre is a rigorous selection of free, legal software for Windows 98, 2000, XP with a easy to use direct-from-web installer.
- Open Source Windows - A simple list of the best free and open-source software for Windows
- 20 Open Source Windows Apps For You - Blog note with a list of 20 useful open-source Windows applications across multiple categories.
- 40+ Free Windows Apps For You - An expanded list of Windows open source software.
- Portable Apps - Suite of portable apps
- Portable Freeware - A good collection of free and open source portable apps.
- winPenPack is an Italian website for portable applications with suites for essential apps, gaming, school and web.