UltimatestarA compound of Ultimate Skewb (hence the name) and Icosahedron Skewb.
X-CubeA 3x3x3 with a concave but regular shape.
X-Cube (Brandt)A 3x3x3 truncated mainly on the edges and stickered like two fused tetrahedra.
X-DinoA shape variant of the Dino cube resembling the X-Cube
X-MegaminxThe concept of the X-Cube applied to a megaminx.
X-RexA Rex Cube truncated on all edges. Inspired by the X-Cube but implemented differently.