ChucK is a strongly-timed, concurrent, and on-the-fly music programming
language.  It is compiled in real-time, on-the-fly, and allows code to be
added and modified while the program is running, without stopping or
restarting.  It is used for synthesis, composition, performance, and
analysis.

ChucK presents a unique time-based, concurrent programming model that's
precise and expressive (with regards to time), dynamic (with regards to
concurrency), and interactive (with regards to interface).  It is open-source
and freely available.

On OpenBSD, ChucK uses the JACK audio server for output.  Start jackd (via
sndio or another backend) before running chuck.

Website: https://chuck.stanford.edu/