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

Hydrogen is a software synthesizer which can be used alone, emulating a drum machine based on patterns, or via an external MIDI keyboard/sequencer software. Hydrogen compiles on Linux/x86 and Mac OS X, although the latter is still experimental, so ask in the developers mailing list for further details.

Website: http://www.hydrogen-music.org