Java, it's the OG and you can use mods. I haven't played in forever though.
How do I join this server?
Go create an account and download the classicube client from
https://www.classicube.net/. Then join Jacob_'s CTF Server. We also have a discord at
https://discord.gg/m9jcnN9 where most of us hang out. If you let one of us know when, we can probably join you to play.