I suppose most of the Maemo 5 FOSS library could be ported with up to date libs at least as a stopgap to get the app repositories populated with QT stuff designed for mobile use.
That would for example mean stuff like modrana for nav and well developed apps for just about every other category.
I am not sure how difficult FOSS android apps you find on f-Droid would be to port over to real gnu-linux, that repo is enough to do almost everything on my non-Google LineageOS tablet.