This is a very simple modular origami design I recently came up with when revisiting my Oxi unit from a few years ago. The unit has folded edges on one side and raw edges on the other, and this picture presents the better-looking side with folded edges. Given the simplicity of this design, I would not be surprised if others had come up with it before independently [update thanks to David Mitchell: Yes. It’s known, usually with folded edges on both sides though.].
See also: Two-Unit Cube II.