Orth is a collection of code for building multiplayer online virtual environments, built atop Narya and Vilya, mostly extracted from Whirled so that we could use it on smaller standalone projects.
We used it for games like Bite Me! and Doctor Who: Worlds in Time and probably some other stuff that I've forgotten in the numerous years that have elapsed since those halcyon days.
Don't even try. I'm sure it has myriad obsolete and long since evaporated dependencies, some potentially internal to Three Rings (RIP). The code is released here mostly for posterity and the morbidly curious.
If you're really crazy enough to try, you'll need Ant and then you can just start debugging the build failures as they arise. If you have serious questions, file issues, but requests morally equivalent to "Halp? I have not the clues." will be summarily closed.