Audacity is an Open Source audio application designed to be a full-featured yet easy-to-use multi-track recording and editing suite. Stable version is also available.

Audacity can record live audio through a microphone, mixer, digitize recordings from other media, and capture streaming audio. Audacity can record, import and export, modify quality, has a ton of built-in effects, analyze capabilities, plug-ins, and much more; we're scratching the surface.

It supports almost all of the popular audio formats out there, including WAV, AIFF, Ogg Vorbis, FLAC, MP3, and FFmpeg-compatible files. Oddly enough, the one format it does not support is M4a, which is popular with Apple and iTunes. If your music library has many songs you downloaded from iTunes, you will need to download a converter first.

Audacity offers some support within the application. It includes quick help (local or the internet), a user manual online, a Wiki page with tips, tricks, and more, and a link to their online forum.