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It is not even on the main website (https://www.platoapp.com/). The only text is "Your space to hang out, find fun & new friends"

Looks like what used to exist as Yahoo! Games a really long time ago: chat rooms + multiplayer games.

That's exactly what it is

Yeah, I had the same question. Here's a video that I looked up. https://www.youtube.com/watch?v=-v2q5XR2Mfk