ADDAC System is a Eurorack modular synthesizer manufacturer based in Lisbon, Portugal, founded in 2009 by André Gonçalves to explore the crossover between analog synthesizers and computers. The company became formally established in 2014 and has grown to offer a catalog of more than 65 modules spanning the ADDAC200, ADDAC300, ADDAC500, ADDAC700, and ADDAC800 series, with its product line focused on hybrid instruments that combine analog circuitry with digital processing.

The brand is known for distinctive utility and sound-design modules such as the ADDAC503 Marble Physics, the ADDAC806 VCDLS, and the ADDAC815 Stochastic Function Generator, along with tape-inspired designs, wavefolders, and granular tools. Their aesthetic typically features black panels with colored knobs and an emphasis on tactile, performance-oriented interfaces.

Development and assembly are handled by a small Lisbon-based team, with André Gonçalves leading R&D alongside engineers including Ruben Costa and Tiago Silva. ADDAC modules have a following in the Eurorack community and have been used by artists including Depeche Mode and Lloyd Cole.

ADDAC System has 11 products cataloged on Equipboard, including Modular Synthesizers and Switch Effects Pedals. Their gear is featured by 4 artists, with the strongest followings in Electronic, Stage & Screen, and Pop. Notable users include Richard Devine, Andrew Huang, and Junkie XL.