Fun small game :)
Played alone and it was surprisingly challenging!
I like the idea and thought the art on the cubes was cute. The way the cubes tilt a little bit when you move them is perfect.
I liked the string physics as well, feels very real.
Well done.
P.S Unity has support for building games in WEBGL format, so they can be played in the browser. I recommend you do that next time and you will probably get more players.