Audacity is open source software for recording and editing sounds. It is a solid cross-platform sound editor supporting multiple formats with an intuitive graphic user interface.

Traverso is a cross platform multitrack audio recording and editing suite, with an innovative User Interface. Its a complete solution from recording to CD mastering.

Ardour is a digital audio workstation that you can use to record, edit and mix multi-track audio. It also allows you to produce CDs and mix video soundtracks, and it’s great for testing out new ideas about music and sound.

Rosegarden is a professional audio and MIDI sequencer, score editor, and general-purpose music composition and editing environment. This is a strong contender when it comes to working with Midi.

Hydrogen is an advanced drum machine for GNU/Linux. It’s main goal is to bring professional yet simple and intuitive pattern-based drum programming.