.rte is an encrypted filetype, like .pcf for Objaction Mover.

My Millennium Catwoman figure in Free Stuff is distributed as an .rte file. I encrypted the hybrid mesh, using the original Victoria and MilCat meshes as keys. The .obj file can't be decoded and used unless someone already has Victoria and the MilCat.

You're not limited to meshes, however. You can encrypt anything, including textures and text files.