I dabbled with Flet for a couple of weeks and all I can say is: I wish it were further along in development. Either that, or had more documentation and examples available. I love that it targets all platforms and that it's so easily distributable, but where I ran into problems was with layouts in general and aligning controls with one another specifically. I was ready to drop all other GUI toolkits before I ran into that snag. Perhaps in another year or two I'll take another look.