This 4x4 door drops the gravity blocks (concrete, sand or gravel) and pushes them up on the sides. Afterwards they will fall down again to close the door. It mixes up the patterns.

I've been building these type of doors for a while and realised it has a lot of potential for diagonal doors, a normal diagonal piston door would be much harder to build.

Feel free to use this however you want, or use the concept for other builds