We know that long term, we will almost certainly not wish to pay Slack’s rates for a paid tier on this project given the open nature of it and the thousands of current members.
This thread exists to propose and compare alternatives.
Alternatives already mentioned:
Personally I would like to forward Discord for some serious discussion. It offers a very robust permissions system, offers unlimited history search, can take webhooks from GitHub and other sources, and is used by other open source projects, some as large as 100,000 users. This is all completely free and requires no infrastructure from us. It’s marketed to gamers and such, but it really is an underrated app for open source projects.