Comment by aexaey

Since nobody mentioned Zulip's REST API yet, I'll do. There is one, and and it is really good.

There are also native language-specific wrappers for that API, for example in python[1], which lets you write a bot in 5 lines:

  import zulip
  client = zulip.Client()
  def onmsg(m):
     print ("at %d, %s said: %s" %
          (m['timestamp'],
           m['sender_email'],
           m['content']))
  client.call_on_each_message(callback=onmsg)

[1] https://pypi.org/project/zulip/