I've got a project with a rather messy VCL codebase built on Borland C++ Builder 6. I intend to rewrite most parts of it since it's hardly maintainable in it's current state. I'm looking for a good and free alternative to VCL. It is a Windows-only closed source commercial project.
So main requirements are:
- Free for commercial closed-source projects
- Manage Windows GUI. Other components (db links and stuff) not required
- Be extendible (so one could write my own GUI components based on existing ones)
- Be STL-friendly.
Please post your suggestions, with pros and cons if possible.
EDIT
Thanks for all the answers. I've decided to go with Qt as it has some other nice features like Qt Linguist translation suite.