Paid-for version: Adobe Audition
Open-source alternative: Audacity
Audacity is a digital audio editor and mixing platform, complete with a graphical user interface and cross-platform OS support. It's one of the most popular open-source downloads in the world.
The good: One of the most common uses of the program is audio file conversion, as it handles a wide range of audio formats, including FLAC and OGG. It's easy to record, cut and edit sounds, remove noise, adjust levels and alter equaliser settings. An array of plugins allow you to extend core functionality, such as overlaying sound effects and samples. Audacity is a superb package for home users who want more control over their audio than the super-awesome-amazing Sound Recorder that comes with Windows allows.
The bad: While it's superbly kitted out for home users and podcasters, it can't match commercial products like Adobe's Audition software for studio recording. The GUI is also rather plain and not as easy to read as some paid-for alternatives.
Conclusion: Be prepared for a steep learning curve, but rest assured it'll pay off. Audacity offers a great set of features and is suited for loads of purposes. If you're setting up a home studio, you'll want to look for something vastly more capable. But for anyone who just needs to record, cut, manipulate and export, it's a killer.
Download it here: audacity.sourceforge.net