FerrumC, similar to Pumpkin, which I recently posted today, is yet another Minecraft server built in Rust that released a month ago. Funny that there’s already an inside joke regarding new Rust Minecraft servers being released close to the pace of JavaScript frameworks.
Nobody has even developed a fully open source Minecraft server in Java yet. There’s never going to be one in Rust. The amount of work to keep up with changes or additions in content or the world simulation would just be too high.
There have been multiple Java based projects throughout the years. The most advanced one that is currently in development is https://github.com/Minestom/Minestom
Yeah world gen is one of the most difficult parts to implement since Minecraft and Mojang are very protective of that area, not to mention the monumental task of maintaining bug compatibility, especially with redstone. It’s still interesting to see parts of Minecraft being implemented in other languages.