I happily use a lot of open-source software.  I do real work with these programs and find them to be every bit as professional as the commercial applications I’ve been compelled to use. I’ll write on these and answer questions as best I can. In the mean time, here is a list of stuff I use. I’ll update it when something occurs to me. It’s not intended to be a comprehensive list of open source software. That’s more like what you find here. It’s a reflection of how I actually get stuff done. It will change and grow as it occurs to me.

OS

• Ubuntu  — Linux is Linux, and I’ve used Fedora, Suse, Slackware, Yellow Dog and others, but my favorite has been Ubuntu.

Office tools

• OpenOffice — I first used this back when it was StarOffice, before they opened the source and the subsequent adventures with Oracle and all that. I still use it and like it. I easily prefer it to Microsoft Office for my needs…which upsets some people.
• LibreOffice — When Oracle started working to restrict OpenOffice several of the key developers forked a new project which was specifically intended to remain free and open. It’s also good (and I like it better than Microsoft Office).
• Firefox — great browser with lots of flexibility
• Thunderbird — Email by the same folks who brought us Firefox. Straightforward and flexible.

Media

• Audacity — a simply outstanding tool for editing and recording audio. I’ve used it for podcasts, sound effects, music editing, and all manner of things.
• Blender — This program is just cool! 3D modeling and animation, video compositing and editing… It requires some devotion because it’s as intuitive as a 1990s CAD program, but the power is immense! I’ve taken to using it more and more for video editing.
• GIMP — Terrible name… Awesome program… It’s a pixel-based graphic editor for things like photos and web images. Extremely powerful and extensible, I’ve used it for all manner of things.
• Inkscape — Another powerful graphic program, this one is vector-based, letting you create designs that are infinitely scalable. It’s great for print designs like business cards or posters.

Security

• KeePassX — This is a great little password vault.
• openssh — This is a way of connecting systems securely. There’s a lot of power in here and I’ve used it to great advantage for remotely supporting systems.

Stuff I’m not sure how to categorize

• Filezilla — Outstanding file transfer tool. It does FTP and SFTP. You can download a file, edit it and it will detect the changes and upload for you.