Looks to me like they just straight up ripped the Discord front-end, changed the parts where it connects to a back-end and hosted it. Registration page has links to Discord's ToS, opening dev tools will give you a message about working at Discord. You can even try to buy nitro on it and it will try to call stripe with what I assume is Discord's key. Scummy as hell.

They're straight up ripping the image background from https://discord.com/login.

Really inappropriate for FOSS.

Without context I would've assumed that was a phishing site.

I checked the site, and really its not "similar", its unrecognizably same.

If I had doubts before, seeing this I lost all faith in this product just like that.

Where was that demo site linked?

The other instances do not rip their frontend code straight from discord.

It's the first link if one visits their website https://fosscord.com/

Looking through the demo site, it really seems like it's just a copy paste of the real thing. It even collects analytics the same way.

This is not how you build a FOSS alternative.