The first thing I can think of is a github and/or a webpage of the project.
Usually bitcoin enthusiasts will prefer open-source projects, and certainly anyone will appreciate a website where we can see more information about the project.
OP could use dual licensing system (such as GPLv3 and propriety) where GPLv3 version only available as source code while propriety version provide compiled application and optionally more feature/support. But it's complicated and usually only big company who bother use such system.
P.S. I know dual licensing system is controversial on open source community.