Hi and welcome! Piggybudget will remain free and will not become commercial. As far as releasing it as open source it is something that could happen in the future but I haven't decided about it yet, it depends among other things on what comments and requests I get from the users.

There are other future projects I am considering and some of those will be open source (for example I may release the web framework I have created to build this website) while others may be more business oriented and may be commercial.