SlowMB

SlowMB is an RMS based leveling amp/compressor aimed for mastering but it can be very handy in production as well. SlowMB does not just reduce the gain when the level is above a threshold, it will also increase the gain when the level is below. With the right settings, SlowMB can be the most transparent compressor you heard.
Its recommended use is just for even out the level of a whole track but can be fun in your drum bus or single instruments as well.