RefinedVanilla is a true vanilla anarchy server where you can do almost anything. The only real rule is no hacked clients so it stays fair in that way.
People build huge bases then other players can find them and wreck them. You can explore far out and just mess around with whatever you want.
It also runs custom software that adds multithreading so it can handle high player counts while still feeling like vanilla. Nether roof is enabled and chunkloaders work and lazy chunk cannons work too.
I found RefinedVanilla and it is a true vanilla anarchy server with basically no rules except no hacked clients. You can build destroy explore and just do whatever you want in a world that stays close to how Mojang intended.
It runs on Fabric instead of Paper or Folia so stuff like redstone TNT pistons and tick timing act like single player. That makes it feel right for technical players who care about real vanilla behavior.
They also have a custom Fabric fork with multithreading to help it handle higher player counts. The server can change simulation distance mobcaps and render distance to keep it running smooth.
Nether roof is enabled. Chunk trailing is patched. Portal chunkloaders can work but they unload when there are no nearby players in either dimension.