Casting lines to inspire others to work with you on a project you care about

Many projects (especially in open source) are single coder hero projects. They trudge on. But to make projects sustainable, developers ultimately need to find ways to cooperate and pool their efforts. (Despite the not-invented-here syndrome). But maintainers often find it hard to inspire other developers to get engaged in the same problems they care about. Everyone has their own pet projects, and time is scarce all around.

Vjeux, known for his work on React and React Native, proposes a solution in the linked post.

It would be interesting with a discussion on what ways have you've found successful in inspiring fellow developers to work with you on a project you care about?