I maintain a list of public servers here: https://m64p.s3.amazonaws.com/servers.json. Any emulator is free to use these servers, as long as the MOTD is displayed to the users.

gopher64-netplay-server also listens for broadcasts on UDP port 45000 by default.

The frontend just needs to send a UDP broadcast with a single byte set to 1 to port 45000.

The server will receive this, and reply with a single UDP packet containing a JSON object in the same format as https://m64p.s3.amazonaws.com/servers.json with its details.