This relay is running my implementation. Grain 🌾. Grain is a highly configurable (probably the most configurable of any implementation out of the box) relay implementation. It's written in Go and uses mongodb as a database. I made it because there were no options that existed there were as configurable as I would have wanted them to be, so I made my own. If you want a taste of all the possibilities of grain you can check out the example configs here: https://github.com/0ceanSlim/grain/tree/main/app%2Fstatic%2Fexamples
It's also extremely easy to get up and running. There are release binaries for Linux and Windows. It also creates the initial configs by itself from the examples when you first run it. There's basically no setup but changing the config to your liking. The database also creates itself, you just need to download and install the Mongodb community edition server, which is super straightforward and linked in the readme.