probably a part of Free Media Tools (e.g. Ardour, Audacity, etc), sound synthesis and/or Algorithmic Music

active/interactive

• sythesis and patterns with Supercollider
• MaxMSP / PureData
• tidal → http://yaxu.org/tidal/
• overtone → https://github.com/overtone/overtone/wiki/Getting-Started
• etc+

discussion/overview/summaries (as of 2015ish) extract→ https://news.ycombinator.com/item?id=10180423