Customizable Reuleaux Triangle, Tetrahedron and Solid of revolution. The picture shows the standard Reuleaux triangle used as a keyring.
You can customize features such as: size, side thickness, height etc.
The Reuleaux triangle is unique - it is the simplest shape of constant width after the circle. It's diameter is constant, however it's radius is not - these properties allow it to be used in applications such as drill bits (to cut square holes) and rotary engines. The Reuleaux tetrahedron however is not of constant width (although it is pretty close). Revolving the triangle around it's midpoint will give you an acorn shaped solid of revolution which is also of constant width.