RMD is a model format. It comprises all of the 3D assets in the PS2 versions of Nocturne, Digital Devil Saga: Avatar Tuner, Digital Devil Saga: Avatar Tuner 2, Devil Summoner: Raidou Kuzunoha vs. King Abaddon and Devil Summoner: Raidou Kuzunoha vs. The Soulless Army. PB contain all of the model's textures and animations in addition to the mesh.
Atlus PB Importer
Developed by TGE, a 3DSMax .PB and .MT animation importer. You can get it here.