Although open source means worse case scenario you can grab the source and maintain it yourself often this doesn’t happen. Many awesome projects just go into obscurity and I’m sure many people aren’t even aware they are no longer maintained. There was no announcement, no project closing, no call for help. The developers just stopped coding, maybe they died, who knows.
I’m starting a blog called Maintenance Required (maybe I’ll do more later) to list software that needs someone to take care of it. I probably won’t find everything, but maybe I can get a few good projects picked up. Feel free to contact me if you know something not on the list.