The Nikon FG was the first to introduce TTL flash on the standard flash hot shoe (the F3 has TTL flash, but uses a proprietary shoe). It was also the first multi-mode Nikon and introduced the Program mode.
The FG is based upon the EM, just like the FA is based upon the FE. Its dimensions, weight, meter, viewfinder, winding and motor drives are all based on the EM.
In the accessory list for it, there was a new TTL flash, the SB-15, a new motor drive, the MD-14 and a D shaped rubber eyecup.
It is a nice SLR.