[torstenvl]

Strongly recommend wxWidgets. It can be slightly rough around the edges for some advanced functionality, however:

- It wraps native components (GTK on Linux), meaning your application remains performant.

- It has very friendly licensing (LGPL and/or a wxWidgets-specific variation, both with an exception for static linking), giving it a large advantage over, e.g., Qt.

- In addition to GUI components, it has cross-platform integration functionality, e.g., you can query the OS MIME/file type manager to get the appropriate command for opening a file in the default handler.