1. Mozilla Firefox (Web browser)
Crikey, another Firefox plug! Yeah, we love the 'fox, and we'll keep talking about it until EVERY SINGLE ONE OF YOU USES IT. It really just doesn't get any better when it comes to a cross-platform, open source web browser.
2. Mozilla Thunderbird (Email client)
Firefox's much less celebrated little brother is one helluva email client. We especially like its customizable message filters, built-in adaptive Junk mail filter and ability to install useful add-ons (like Firefox).
3. Open Office (Office suite)
Used to be that anyone who wanted to open a Word document had to drop a few Benjamins on Microsoft Office or risk pirating it. No more - Open Office is a free alternative to M$ Office for students, freelancers and poor people just wanting to save their spreadsheet as an .xls.
4. Gaim (Instant messenger)
Chat on any service you'd like - AIM, Yahoo! Messenger, MSN, Jabber, ICQ - with this multi-platform, tabbed IM client.
5. ClamWin (Antivirus)
Norton bugging you again to break out the credit card and subscribe? Uninstall! ClamWin is free anti-virus software with automatic updates and scheduled scans, no credit card required.
6. VLC Media Player (Audio/video player)
Got a video or audio file Windows Media Player or Quicktime can't play? Betcha VLC can.
7. KeePass (Password manager)
Another app you really don't hear a lot about, but for anyone with more than 6 different passwords, KeePass is indispensable. Check out my previous feature, Securely track your passwords for more on using KeePass.
8. Cygwin (Unix command line emulator)
That DOS command line just doesn't cut it. Wanna turn into a CLI ninja on your PC? You need Cygwin.
9. Eraser (Data deletion utility)
Before you donate, sell or trash your hard drive, you want to make sure there are no traces of your naughty private data on it. Eraser uses the same algorithm the government uses to wipe your hard drive clean.
10. TrueCrypt (File encryption utility)
You've got a folder full of files you don't want anyone to access but you. Lock it (or an entire thumb drive) up with the free TrueCrypt software. Check out the previously-posted Encrypt your data article for more on using TrueCrypt.