This server is built around a project called Pyrium which is a server side meta loader. It is made so people can mod the server using Python style code but it still runs fast like normal Java stuff.

From what I see Pyrium does not just run slow Python. It compiles the scripts ahead of time into its own bytecode and then a virtual machine inside the JVM runs it. That way the server gets clean Python like syntax but it is still focused on performance and safety.

Each mod runs in its own virtual machine so if a script goes crazy with loops or memory it can be stopped without crashing the whole server. The VM can watch the instruction count and just halt a bad mod which keeps the main server stable.

There is also a system that builds the resource pack for you. It looks through the mod folders for asset files adds namespacing automatically and then merges everything into one zip pack for players so you do not need to mash zips by hand.

Server versions and loaders are managed through a json file. In that file you can say if the base loader is paper or forge or fabric or vanilla and if it should auto update and how the resource pack is handled. Pyrium then pulls the right files and manages it for the server owner.