The original groovebox for dance/techno! It's got 303, 808, 909, Jupiter, and Juno sounds. It is a sequencer arranger with looks inspired by the original 303's and 808's... Not to mention it includes real-time Filter Cutoff, resonance, panning and arpeggiator. It has been used by ATB.

The key features of the MC-303 are:

Sound generator with 24 note - voice polyphony
8-track sequencer (7 pitched instruments and 1 drum kit)
8 part timbrality
448 preset sounds and 12 drum kits (includes the Roland CR-78, TR-808, TR-606 & TR-909)
Reverb/delay and chorus/flanger effects
300 onboard dance music variation patterns such as drumbeats and basslines
Recording length of up to 32 bars per pattern
Instant storage of up to 50 user patterns, 300 pattern variations and 10 songs
Storage space for up to approximately 14,000 notes
MIDI in and out connections (but no MIDI thru)