The content ends at the space shuttle. In a previous version, repairing the space shuttle unlocked aliens, but the author merged it out with their final update.

However, I'd recommend you stop playing (or start cheating) after you repair the laser gun as the progression grinds to a halt. There's only a couple things to unlock after that, none of which are particularly interesting.

Also, there's 2 achievements that you don't seem to be able to get: Say Cheese and OCD Hell. I looked at the code and I can't find anything that unlocks them. I think cheese is an unfinished feature. There's an unfinished task in the github issues that mentions it. OCD Hell is probably to troll people that will go crazy that they can't get every achievement. Heh.