Blue Square Models produces 1/72 resin kits of the so-called Paper Panzers, vehicles that were only projects and never got out of the drawing desks.
This kind of vehicles, which are not completely fictional but were never built, has become more popular in recent times.
Blue Square catalogue has now fifty of these models, including tanks, self-propelled artillery, Jagdpanzer and even an armoured ambulance on a Panther chassis.
Some kits include also photo etch details or feature interiors.
While you can see here a few examples, the whole catalogue is available at their website