Xenon Minecraft is a Minecraft Server implementation written in kotlin. It doesn't use any of Mojang's code whatsoever so nothing is complicated to communicate with. It's API is planned to be very easy to use. You do not need to use our API if you do not want to though :).
Xenon Minecraft also strives to support multiple minecraft versions and types. Having builtin support for allowing multiple versions to connect to your server. This would usually require a plugin like ViaVersion. We're also adding support for allowing both the Java edition and Bedrock addition to connect! Obviously certain features would need to be restricted, such as redstone possibly and other things, especially since the versions are different in a few areas and mechanics.
We also plan to include a separate sub-project which is a proxy, it'll be almost exactly like BungeeCord and its forks except it'll be made specifically for the Xenon Minecraft Server Software. It will allow you to keep your servers in online mode. When enabled in the settings of the actual game server software you can set it to specifically only allow proxy connections. Although there are better ways which would be setting up firewall rules properly so those servers can't be accessed and only the proxy can be connected to.
You can find information on these references here: