There are many options. The appropriate mix would depend on the project, popularity, target audience and skills/interests of the maintainer. Off the top of my

There are many options. The appropriate mix would depend on the project, popularity, target audience and skills/interests of the maintainer. Off the top of my head: Hardware, hosting services, support, trademark or patent rights, custom development, consulting, features (open core), bragging rights, social/insiders club membership, swag/merchandise, educational materials, certification, job placements/recruiting/headhunting, marketing/ads/product placement.