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When Mark Wainwright visited his friend Francis Irving in Liverpool last May, he nearly locked himself in his small guest room just beneath the attic. The door was missing a knob, but it could still latch shut. Wainwright, a community coordinator with a U.K. non-profit group, wanted to let his host know about the problem. So he filed a bug report on GitHub.

“The almost-attic room has no handle on the door,” Wainwright wrote. “It would be simple to add a handle and would prevent someone getting locked in the room – quite easy at the moment as the sprung...