Thank you everyone for the feedback and especially to Terrence for his code and getting these releases out.
The next thing that needs fixing is to make it load a puzzle automatically when clicking on a .puz file. I think this just means having a correct .desktop and .service file, which I have tried to do, but somehow it still doesn't work for me.

After that I want to have a built-in browser, so when you have a whole bunch of puzzles downloaded, you can select one by title and maybe percentage completed.