I used Piazza in the past, but I was never happy about their selling student information, so on Shriram’s recommendation I switched to Campuswire last fall. It went fine (it is comparable to Piazza, not identical). Not happy about Piazza’s pivot to ads and subscriptions and I will not go back. My institution has paid for a Piazza subscription for the term about to start (we’re a heavy user and could negotiate down the initial price) but is actively looking at alternatives. Campuswire had to pivot away from subscriptions (they found they were locked out) and are currently trying to sell courses, which good luck to them but I don’t think it will sustain them. There’s a possibility we will pilot EdStem so I may use that for winter term; otherwise I will use Campuswire.

I like Zulip more than Slack, but both of these are IRC-like and not drop-in replacements for the more narrowly-focussed services mentioned above. I could run a course on Zulip (and am prepared to do so if everyone else disappoints me, which is definitely possible), but it would mean adding structure not inherent in the tool, and I would not recommend it to colleagues who just want everything to work easily.

I’m an undergrad and took a class utilizing CampusWire in Fall 2020, and had very few issues with it I’ve never used Piazza so I guess I don’t have a good frame of reference