The Volt has a unique transmission, and above certain speeds, to keep the EV motor from over reving, it starts to take power from the engine, rather than being all EV driven to the wheels. Depending on your driving situation, you may never engage that mode, though - it occurs at a moderately high speed. So, it can change from an EV, to serial hybrid, to a parallel one. As far as I know, that's unique in the world as well, but, the i8 is sort of like that, but the two axles are not interconnected, so it's either all EV, or both, but neither directly connected except for the generation of electricity. So, there's more than one way to skin the solution to moving.
There are some others that are planning a system similar to the i3's REx...Mazda is planning on using a rotary engine as a serial hybrid solution. There may be others, it's too early to tell.
2011 535i x-drive GT, 2014 i3 BEV