Discord did a complete R&D (rob and duplicate) of Slack and focused on video game communities. It’s doing very well from what I can tell!
I haven't heard this term before, but I'm not sure it is a "rob and duplicate" if they are targeting a market segment that Slack never advertised towards nor was really designed for. Seems more like refreshing Slack for a niche, but it turns out to be a really big niche.
It's Slack + low-latency voice chat. With vastly less hassle than Teamspeak/Mumble/etc. Recipe for success right there, though I'm not sure how well their monetization has gone.
You would think Microsoft Teams would beat them, but they inflated it with Office 365 "Features". In comparison, Slack feels more like a complete product the first time you use it. Any other must-haves for your organization are treated as add-ons.