"Enter Hydrogen, the free, open source advanced drum machine
built for Linux. It comes bundled with a good variety of
pre-installed drumkit sample sets, all modifiable and expandable.
After you've chosen a drum set to use, you've got a pattern editor.
Drum patterns can be as fast or long as you desire; from there, the
program's song editor can be used to string multiple patterns
together to create a complete drum track for use in a song, which
can then be exported to WAV for any other program to use."