Tidal Cycles (or 'Tidal') for short is free/open source software written in Haskell. Tidal is using SuperCollider, another open-source software, for synthesis and I/O.
Tidal Cycles allows you to make patterns with code. It includes language for describing flexible (e.g. polyphonic, polyrhythmic, generative) sequences of sounds, notes, parameters, and all kind of information.
Tidal is used by a large community of musicians for composition, improvisation and exploration of algorithmic music. Share, explore, join an algorave, compose your next track, make music.