Today I tried Merkaartor, a mapping application built using Qt 4. Although it can fetch from openstreetmap and upload it again, the site states that it can not save anything to disk yet. Features I miss are satellite / aerial photo (like google maps) and layering.
Sadly, the author said
I cannot make any guarantees if I will improve on this. It started out as a test project to get acquainted with Qt4. I know Qt4 now.
This is a good piece to anyone who wants to extend it.