1. I feel biased towards Zulip because it's open source, it's Python, and I know the people who made it, and I don't want their creation to die. But the UI is a little more complicated than needed (the "topic" feature in particular) if we're just going to do this as a single social channel.
2. I can handle Discord just fine nowadays but *please* don't combine this with the Python Discord server. That server is super active with learners and teachers, and has hundreds of channels and it's just really hard to ignore that activity if all you're interested in is a single channel. At this point I'm sure Kyle will pop in with instructions for how to permanently hide all the other channels, but I still say it'd be way easier if we had our own small server so nobody would have to hide anything. (And "server" is purely a virtual thing IIUC, we don't need hardware or even a dedicated VM. If there's a fee I'd be happy to pay for it personally, if that's what would stop us considering this option.)
3. Gitter is totally fine for this too.
4. Discourse is different. It's trying to be a better email, not a better IRC. I think that disqualifies it for this particular purpose. (Also the UI is too rich for the purpose.)
5. I can handle Slack too, but Slack doesn't really care about open source users, so let's not bother with them.
6. Teams? Please no. I use it every day for work, and it's great for video conferencing, but the group chat is terrible. Trust me.
7. IRC? I have had bad experiences here in the past, and I will never use it again.
8. I would want a purely *social* chat that is *closed* to non-core-devs. Everybody who can read it should also be able to post, and feel free to do so. As soon as there's the possibility of spectators I clam up, or at least I am much more guarded about what I post, defeating the purpose. (There should be a CoC that includes "no posting elsewhere of what you see here ever".) We already have enough channels where technical discussions are archived for posterity. We should be careful not to have discussions that lead to decisions on such a chat channel, because that excludes others who either weren't there at the time (all chats are terrible when there's a lot of scrollback, almost by design) or who just choose not to participate.