"Supercar" can be defined several different ways. Some might define it as ultralightweight + perfectly powerful engine + proven racing marque + outrageous bodywork. I am one of those people, and I am nominating the Lotus 340R.
Built on a modified Elise chassis (what car isn't these days), the wet weight of this beast was 1500 lbs. With a four-cylinder engine making 187 hp, the 340R had a power-to-weight ratio better than that of a BMW M3.
It wasn't faster than a Koenigsegg or as nimble as an Ariel, but dang if it isn't a heck of a fascinating Lotus, and a deserving contender for Obscure Supercar Friday.