A square can bound a cube or a heptacube if a cube is glued to each face. An equilateral triangle can bound a tetrahedron and other shapes.
The diamond (2 equilateral triangles) can make a trapezohedron.
Less obviously, the L-tetromino can bound an infinite spiral tube.
The 4-iamond can also bound an infinite spiral.
The l-tromino can bound infinite space.
What infinite 3D shapes have faces that are all the same concave polyform? All directly neighboring faces should be in different planes.
What finite 3D shapes have faces that are all the same concave polyform? All directly neighboring faces should be in different planes.