Hydrogen
Hydrogen is a free drum machine for Linux/GNU. Its features allow you to make your drum beats professionally, but without having to pay for them. The easy-to-use graphical user interface allows users to intuitively make their beats.
Hydrogen has a built-in sequencer and mixer, allowing you to layer up to sixteen samples for each instrument. And with a wide array of supported files, you can easily be your own DJ with Hydrogen.