It looks similar to a modified Minecraft.jar file.
It contains a META-INF folder with a MANIFEST.MF,
On the main there's also a folder called load containing: an extensionless file called ID, a .class file called JarMain, and another MANIFEST.MF.
And also on the main a folder called plugins exists, containing a file called unrecomserver.class.
Evidently it's some kind of Minecraft modification.
Quickedit: Virustotal claims it's clean. I'm not unpacking it for safety reasons though.