That's a lot of open source software
For my job as developer I recently used Eclipse, Subclipse, Notepad++, Maven, Maven plugins, Apache Cocoon (and 1 million other Apache projects), ROME (Atom/RSS), Xinha, Prototype and script.aculo.us just to create, compile and manage code. Image editing is done in Paint.Net, Hippo CMS to manage the content in Hippo Repository and MySQL. To access them directly I use SQuirreL or WebDAV pilot. Firefox, Web Developer toolbar, Firebug, Solex and TCPMon help me testing and debugging. Depending on the platform PuTTy, iTerm.app, WinSCP, FileZilla and Cyberduck connect me to the servers.
To make my computer more complete or for entertainment there's NeoOffice & OpenOffice.org, Adium & Pidgin, Vuze, Growl, Launchy (can't wait until the OSX release), Synergy, Last.fm and VLC.
All this software has one thing in common: it's open source.
My operating systems are Windows XP and MacOS X because I grew up clicking icons instead of typing commands. Ubuntu is still less intuitive to me. I mail with Outlook until Thunderbird has better support for appointments in Exchange or Evolution is available under Windows. oXygen helps me writing XML, XSLT and CSS. I also test in Internet Explorer because most visitors use it. Charles is a great proxy tool for debugging. I happen to like iTunes which came with MacOS. I watch online video in Adobe Flash or QuickTime.
Hmm, my closed source software list is a lot shorter.