SimpleX is an mathematical educational portal and organization. In geometry, a simplex is a generalization of the notion of a triangle or tetrahedron to arbitrary dimension. We started from a tetrahedron, which is a polyhedron composed of four triangular faces. To be a little bit more abstract we positioned the tetrahedron in space and removed a side. In this way the shape is still recognizable, but necessitate a little mind-work to figure it out.