FM10: Not made by Nikon. Go into a camera store and ask to see the FM-10, any Vivitar SLR they might have, the Olympus OM-10, any inexpensive ($200 w/ lens) manual wind 35mm SLR. You'll easily notice that they are all the same camera with minor cosmetic differences and different lens mounts. This is a no frills 70s/80s design 35mm SLR with a pretty crappy meter in my opinion. Of course it'll still use good Nikon lenses, and as always, equipment isn't everything.
FM3a: Latest version; I'm more familiar with the FM2. This was, and still is marketed for the advanced amateur/beginning pro photographer. Very nice camera. I'm sure the FM3a is similar, probably with better meter.
F3HP: moan... this is the coolest 35mm SLR there is in my opinion. Built like a tank. It keeps working when the batteries die. Solid steel with a titanium version available. It's the combat camera. It has everything you need in a manual wind pro 35mm SLR and invincibility (at least compared to most cameras). I've seen F3s that look like they went through a log chipper, but they still function silky smooth. All sorts of modifications and interchangable parts and accessories. Some day I'll add one to my collection; I don't need a Leica (although it'd be nice), but I need a Nikon F3.