Out of all the modules available, effects units are possibly the most widely varied. These come in many styles and types, so let's deal with a few of the most common here.
Perhaps the most widely used is reverb. Spring reverbs,array of digital reverbs. Some replicate plate reverbs or older, classic digital reverbs, while others take things into new territories. Recently modules have appeared that take reverb further than ever, offering effects like shimmer and glimmer that accentuate harmonics and produce beautiful soundscapes, often with built-in modulation.