They were switching from a discord. I don't think they found any option functional enough. Do you mean coracle private groups? What's the other private group messaging thing, I forget (?). Neither are really ready enough or have adequate features for this scenario, maybe. They wanted off discord with little hassle and the same / similar functionality. ¯⁠\⁠_⁠(⁠ツ⁠)⁠_⁠/⁠¯ What would you have suggested? One of them had a look around various options but didn't find a good fit.

We don't have a Discord style client yet, but a proof of concept is available using NIP-29 at

Groups

This isn't for production use. Private groups can be used on Amethyst and Coracle and probably other clients too? Though this standard will probably go away as clients move to adopting NIP-104. Checkout Oddbean.com of you want a Reddit or forum style client.