Softube - Saturation Knob
The free plug-in Saturation Knob is a modeled output distortion that can be used anywhere you need some grit. Use it to fatten up bass lines, add some harmonics and shimmer to vocals, or simply destroy your drum loop.
The three modes, Keep High, Neutral and Keep Low give you three kinds of characters of distortion. If you want to squash a drum loop but keep the bass drum fairly intact, you can for example use the Keep Low mode.