I think the answer is:almost all of them, especially if they are more maintenance than new development. In open source, it is common for huge projects to have

I think the answer is:almost all of them, especially if they are more maintenance than new development. In open source, it is common for huge projects to have a very low dev counts. At devoxx, I heard the maven core, critical for most of the Java world, had 10 devs. This is a lot, compared to tons of lesser known libs. In the enterprise, it's not much better. I know about a library connecting COBOL to the outside world. Half Europe's banking, state and healthcare are critically dependent on it. But its so old and arcane, only a few devs dare still touch it. This is normal for software maintenance. If it's abandoned and still relevant, someone will take over because they have to, and the rest of us become freeloaders. If there already is someone doing maintenance, he will receive a never ending stream of bug reports and even nastygrams.