In person, it's somehow easier to tune the office chatter in and out as needed to keep track of what your colleagues are up to. I have yet to find an electronic replacement for this phenomenon. Email, if nobody thought to CC you, you simply won't find out. If people deal with this by defensively CCing everyone, you drown in email. Slack's value is inversely proportional to its uptake: The more people talk on it, the more it resembles a sort of workplace Twitter where it's simply impossible to try and keep track of what everyone is saying, so you give up and resort to only looking at it when you're trying to slack off. Threads attempt to work around this by replicating the problems of email in a chat app.
I suspect that an old-school web forum like phpBB could work well, but any technical merits won't overcome the social perception. There's just no getting around the nerd factor there.
The only technique I've seen work well is the manager-as-dispatcher approach. This poor soul becomes the designated firehose-drinker. They get CC'd on every email, and they subscribe to every Slack thread. They keep an eye out for anything that Sam or Pat might want to know about, and check in to make sure that Sam or Pat is keeping an eye on it.