Audacity

Audacity X is one of the most used audio editors due to its multiplatform character. No matter if you use Linux, Windows or Mac, you can enjoy its features on any platform and it's totally free. Furthermore, it's multitrack and multiformat, that means you can work with different tracks and formats at the same time and save the output file as any audio format. If you have a mixer or a microphone you can use them as audio inputs for your audio creations. It can capture up to 16 different channels at once. Audacity X supports WAV, AIFF, AU and OGG Vorbis. If you want to work with mp3 files you'll need to install LAME encoder. Cut, copy, paste, add echoes, fade, inversion,... do whatever you want and create your own audio masterpiece. If you think these features are not enough for you, install some plugins and power it up.