The original D&D dice were the 5 platonic solids, the 10s were added later. But there are lots of shapes that can be "fair". You can stick 2 pyramids with any number of sides together, you can make a long prism with any number of sides since it will never land on the long ends, a coin can be considered to be a 2 sided die. I seem to recall somebody made a 30 sided die where the sides were parallelograms, although I never had one.