Tetrahedron Command
 Tetrahedron( <Equilateral Triangle> )

Creates a tetrahedron having as base the given equilateral triangle.
 Tetrahedron( <Point>, <Point>, <Direction> )

Creates a tetrahedron having the segment between the two points as an edge. The other vertices are univocally determined by the given direction, that needs to be:

a vector, a segment, a line, a ray orthogonal to the segment, or

a polygon, a plane parallel to the segment. The created tetrahedron will have:

a face with the segment as an edge in a plane orthogonal to the given vector/segment/line/ray, or

a face with the segment as an edge in a plane parallel to the polygon/plane.

 Tetrahedron( <Point>, <Point>, <Point>)

Creates a tetrahedron with the three points of the first face. The points have to draw an equilateral triangle for the tetrahedron to be defined.
 Tetrahedron( <Point>, <Point>)

Creates a tetrahedron with the two points of the first face, and the third point automatically created on a circle, so that the tetrahedron can rotate around its first edge.
Tetrahedron[A, B] is a shortcut for Tetrahedron(A, B, C) with C = Point(Circle(Midpoint(A, B), Distance(A, B) sqrt(3) / 2, Segment(A, B))). 
See also Cube, Octahedron, Icosahedron, Dodecahedron commands. 