answer:Probably depends on how you licensed the open-source. Some allow you to sell it while others don’t. If it’s open-source a lot of people will probably get around paying for it anyway. And, people HATE it when you start charging for something that used to be free. I would expect a serious uproar from whatever users you currently have if you decide to start charging for it. One option might be to leave the current version free and let people know you’ll be charging in the future, or charge for a “pro” version with more features while still having a simple free version. Or, develop a new application that you charge for that is completely separate.