I am looking for a chat app on Android and iOS where users join a public room anonymously (no phone number or authentication is required) and chat. If two users want to chat privately, they can chat in a private room. There can be 1 or more moderators who can delete unwanted messages or kick out/ban users.
If there's a server part to it, I prefer it's open source using .NET so I can customize it if I want to, and it runs on Windows. I don't know Linux.