The Roland MC-303 Groovebox is an 8-track MIDI Microcomposer containing PCM samples of both drum and synth sounds. The sounds can be tweaked to a degree, but since they're samples they don't sound as good as the originals created by analog oscillators, modified by ADSR envelopes.

Regardless of what detractors say about the MC-303 concerning sound quality, programming, and its use in a "professional" environment, the little silver box is a lot of fun. Even with the cheesy built in presets it's easy for anyone to play patterns by muting in and out parts on the 8-track sequencer. One preset in particular "B-33" had to be banned at our house because friends who stopped by would end up tweaking that hip-hop pattern for hours on end.

The all in one Microcomposer concept (sequencer + sounds) can also be seen in the Roland MC-202 (analog sound source with digital 2-track sequencer) and the MC-505 (Modified Roland JV-1080 sound source with 8-track MIDI sequencer).

Note: The MC-303 is not a followup to the infamous analog TB-303, and sounds nothing like it.