Great 1990s drum module. The RM50 is the rack version of the seminal RY30 drum machine. Some glowing reviews of it here: http://www.sonicstate.com/synth_reviews/rm50/
This unit has only been used at home and has just been taken out from a cupboard where it has lived for the last 12 years.
Slight dent in the LH rack mount (shown in detail image).