I honestly find this game really annoying to play because of the precision required to solve the puzzle and the lack of precision of the inputs. In level 11, you have to break the string within an inch of one edge for one of the broken edges to reach far enough, but you don't even have time to move your cursor back up to try to "catch" the square. Which means you have to make a very precise shot with a very imprecise slingshot.
The ending is buggy. When I got up around wave 48, the preview thing showed waves after 50 with NaN ships. And then, when it was actually time for wave 50 to attack, it would randomly rewind and send some other wave that I had already killed, and I never actually got to wave 50.
(I don't know if it makes a difference, but I'd clicked the "Send next wave" button a bunch of times throughout the game.)
 "String Theory 2"){kind=icon}
 "Get Off My Planet"){kind=icon}