Maybe not what you meant, but I immediately thought of SaaS. Or various companies' policies of open sourcing non-core software. Both of those are along the lin

Maybe not what you meant, but I immediately thought of SaaS. Or various companies' policies of open sourcing non-core software. Both of those are along the lines of "I need code to do this thing, but I don't want to be the (sole) maintainer." You could write your own language, IDE, OS, build system, source control, networking library, logging library, shopping cart, payment processor, etc.