If crumb is free and open to community suggestions, why not make the product open source? It would allow developers to more directly contribute to improvements and respect user's software freedoms.
Perhaps the author would consider opening up just enough that the community can contribute the code to add elements to the parts catalog, as that seems the most critical.
Some people like to keep their personal projects, personal.
I see no fault of that. This is Mike's project, and if he would like to work on it himself, as opposed to letting other people modify his code, that's his choice.
As a programmer, I do generally open source 90% of things I make, but I definitely have a few projects that I keep to myself.
I agree, this seems like a product that would be open source. Seeing stuff in the planned section on the development page made me want to contribute as some of it is *right* up my alley. There are many examples of apps that are paid to download, but have source code available to allow community contributions. Some examples are Tampermonkey ($1.99), Cyberduck ($23.99), Cryptomator ($11.99), MarkText ($2.99) or FSNotes ($4.99)