Oh man, Slack really is a beast isn't it? I do like the multiple network nature of it (even though everything is saved to Slack's servers) but I find it hard to believe it does so little for it's footprint.

They too though made a Google-like transition and went from an open protocol (IRC/XMPP) to a closed/custom API. At least here, the server admin can enable those protocols if they want and the API seems to offer enough features that someone could probably integrate Slack into another IRC-like client.