Audacity. Open source audio recording and editing
If you need to record a podcast, or you want to record vocals for a song, the most popular option that is open source and free to use is Audacity. It’s not even close to Garageband or professional DAWs (Digital Audio Workstations) like Pro Tools or Logic Pro, and it probably never will be, but it’s perfectly capable of recording and editing audio on Windows, Mac and Linux. It lacks proper VST support (it can use some VSTs, but in an awkward and half-backed way), and it may not win any usability awards, but its easy enough to use and is very stable.
Here’s an intro tutorial on recording and editing with Audacity: