As far as crafting them goes, I think you should have to put a piston in the middle sticks in each of the cardinal directions a piece of Redstone dust, a slime ball, a lever, and a powered rail in the corners (the exact position doesn't matter). They should be linkable, and work like sticky pistons in that they use slime blocks to hold multiple blocks together (I also have an idea for a sort of glue that could be use instead of slime blocks it's in another thread). This design could also be used for decorative purposes. I think it should look like a piston with a roundish head that kinda looks like a pirate ship's steering wheel. You could even make a dance floor using armour stands (this would utilize the way you can have an armour stand change stance with a varying signal strength, but would actually be able to make them appear to dance, rather than just move their arms and legs). The block could be useful for making working vehicles, windmills, waterwheels, etc.

It could have an interface that allows you to control the direction, speed, and range of motion. A better idea for a block with a similar function would be a spinner block.

Minecraft angled slime block launcher