There are actually a lot more totally FREE projects out there, not just OpenOffice, that can replace commercial options. Just search for Open Source, beware the freeware and trials since they often contain spyware. Stick to Open Source (GNU/GPL, etc).
GIMP for example (Gnu Image Manipulation Program) is an excellent replacement for the bloated and unbearably slow Photoshop, though with less features, it has a far more user-friendly interface than PS and is cross-platform.
Then there's Blender/Wings3d (for 3d apps), Bazaar (for SVN), FireFTP (for FTP), VLC media universal media player, Inkscape (Vectorial graphics), FoxIt Reader (recommended replacement for Adobe's reader for PDF files, which is very very unnecessarily bloated and SLOW), Spybot Search & Destroy (Antispyware), 7Zip (recommended replacement for WinRAR and WinZIP, it compresses smaller and is faster, as well as being able to open almost every type of archive files that exist including said .rar and .zip files), etc.
And of course, our favorite, Firefox