I know it has been a few months since we have had a Tiger 1 and a while since a new Sherman, but i do not mean those type of vehicles, so stay away Sherman and Tiger 1 geeks. I will start off with 2 below,
Dicker Max - 10.5 cm Self Propelled Gun, 2 manufactured and only 1 saw action.

and
The British Archer 17llb Antitank gun. Fare enough not that niche, there were 655 manufactured, but it rare we see a British WW2 AFV .made by anyone........... Plus it was a cool vehicle, with the gun fitting and firing rearward, so easy to shoot and scoot.
Dicker Max - 10.5 cm Self Propelled Gun, 2 manufactured and only 1 saw action.

and
The British Archer 17llb Antitank gun. Fare enough not that niche, there were 655 manufactured, but it rare we see a British WW2 AFV .made by anyone........... Plus it was a cool vehicle, with the gun fitting and firing rearward, so easy to shoot and scoot.