Unicorn is a Rack HTTP server to serve Ruby web applications on UNIX environment.

Their system administrator Sam Saffron noted Unicorn was reliable, as it reaps unresponsive workers.

[5] Unicorn inspired other projects like Gunicorn, a fork to run Python applications.

[6] The Heroku hosting provider recommends since 2015 to migrate from Unicorn to Puma.

[7] Deliveroo published a benchmark comparing the two servers and concluded “Puma performs better than Unicorn in all tests that were either heavily IO-bound or that interleaved IO and CPU work”, but that Unicorn was still slightly better performing in pure CPU situations.