[thwarted]

Unless you have a very willing hacker willing to build the integration from scratch, IRC is bad.

There is a hurdle here, but it's not so bad if you're already willing to run your own IRC server. I wrote nodebot[0] to allow machines and scripts to send messages to IRC, it would be a day or so to put an HTTP request handler (apache with a CGI even) in front of this, slap some TLS and http auth on that URL, and expose a webhook that these external services could hit.

One of the great things about slack is that many integrations already exist, so it's often just a matter of sharing an API key or some other credentials between the services, and anyone can do that. I do, however, run into issues with things like github which has many outgoing integrations with services that also use github's incoming API. It can quickly become a mess -- where should the authority lie for doing integrations: with the chat app or with the individual services?

[0] https://github.com/thwarted/nodebot