Modular synths have a long history—at its inception, analog synthesis was by necessity modular. Exploring systems connecting discrete oscillators, filters, envelope generators and noise circuits shaped the building blocks of what we expect in synthesizers today. Originators like Bob Moog and Don Buchla experimented with different modules and formats, but improving technology and market forces quickly shaped synthesizers into predominantly fixed, unified instruments. Starting in the '90s, boutique builders began to revive the modular designs of yesteryear. The trend quickly blossomed into a variety of formats (such as Eurorack) and focuses ranging from DIY recreations of past designs to open formats focused on driving synthesis into new territory. You can find the best range range of modular synths at Industrie Music, from modern MOTM, Eurorack and 500 series modules to vintage units from Moog, Buchla and Roland.