There's a number of free applications out there which are every bit as good as similar ones you pay for. Here's a list of common ones that I've used and recommend:
Avira AntivirusA great, lightweight antivirus suite. I use this on my home PCs.
AVG AntivirusAnother great antivirus suite.
AudacityFree audio recording software. Adequate for simple recordings.
ReaperA "free to try" program for larger recording projects. I use this for my own music production. Its not demanding on system resources and has a lot of great built-in plugins. Even after the trial period ends it remains fully functional.
FirefoxA free internet browser, serves the same function as Internet Explorer, but a little safer since Firefox isn't part of the Windows operating system. Its also highly customizable with addons and themes.
OperaAnother great internet browser. Again, a little safer than Internet Explorer. I just prefer Firefox.
Open OfficeA fully-loaded Office suite. This will do everything Microsoft Office will do. It will even edit files created in Microsoft Office (Word, Excel, etc).
LibreOfficeThis is very similar to Open Office. In fact, its creators once were programmers for Open Office. It's a very good office suite and completely free.