Offset HexAn offset version of Minimal Hex that makes six triangles disappear.
Offset OctaA puzzle related to Minimal Octa reimplementing Star Trap in a minimalistic way.
Oh CubeA puzzle looking like a 3x3x3 but it is indeed a corner turning hexahedron.
Opposition CubeA 3x3x3 designed from scratch. It is related to the Constrained Cube.
OrchidA puzzle with multiple origins, nineteen different moves in three different sets.
OrganolabacusAn extremely big variant of Astrolabacus with eighteen segments but with six channels of beads.
OsCubeA 2x2x2 which uniform tiles retract or extended when the puzzle is turned.
Oskar's Danger CubeAn extension of the Caution Cube or Geared Mixup concepts - this time with more types of moves possible.
Other 4x4x4 (aka Puzzle 19)Designed to be a 4x4x4 with exposed new theoretical pieces. Although it has 64 pieces it presents itself as a superset of the 3x3x3.
Over-and-UnderThree rings with seventeen marbles each, unconnected but exchangeable.