One reason not to use Slack for FOSS projects that isn't mentioned in the article and has had few people mention here: choosing between short history or ridicul

One reason not to use Slack for FOSS projects that isn't mentioned in the article and has had few people mention here: choosing between short history or ridiculous expense. The free version of Slack only has a 10k message limit, which runs out very fast with a user count in the 3-figures range. So if you want history, you need to shell out $8/user/mo, which is ridiculously expensive for chat. And not something a FOSS project should be spending it's limited funds on. Slack has been successful because it's onboarding process is buttery-smooth. They've put a lot of work into making everything easy, from signing up to installing integrations. Unfortunately those integrations also waste a ton of space in the chat window. I use Slack at a couple of companies, and each of them got excited, installed a couple of integrations... and then abandoned the channels with integrations, because they waste so much screen space and you can't follow the flow of a conversation. It's a pity Hipchat got caught napping - they did displaying integrations well. Another FOSS-specific problem with Slack is that they don't have a linux client, so you have to use the web app, which is terrible when you have to track more than one Slack team - you have to manually switch teams to check for updates, which takes a non-trivial amount of time (and the 'switch' control is right next to the 'sign out' control, which I've accidentally hit a couple of times)