[dvanduzer]

I mean, you can call the APIs locked down if you insist, but SaaS is SaaS. Would you count S3 as a locked down API, for example? OpenStack's Swift (and plenty of other products) will emulate it. I chose the term "interoperable" specifically instead of "API compatible" but I agree this gets very confusing when talking about SaaS.

In order to do what Slack is doing, they have to be somewhat committed to open standards. They are just doing webhooks, like GitHub does. We tried specifying microformats, and we tried specifying webhooks, but the "loose RPC" model... Seems to work way better than XMPP server interoperability ever has.

I recommend this recent nested Twitter ("new crowd") thread amongst Stewart Butterfield and many other early web folk, about whether Slack is a web app: https://twitter.com/stewart/status/961704310613491712