[b6fan]

Lazarus / LCL. It is cross-platform, lightweight (more lightweight than Qt since it uses native widgets), can be used for commercial purpose, and is fast to compile.

The limitation is mainly that the widgets are limited. For example, comctl32.dll hasn't got new widgets since Windows xp. So depending on your needs, it might fit perfectly, or lack some features and that's going to be painful.

The Pascal language will feel outdated. But you don't have to do everything using it. You can, for example, write the non-UI logic in other languages and then glue them using dynamic libraries.