I am looking for a cross platform gui library that can be used to create dialog boxes, that must fit the following requirements:

1. Be written in C or C++.
2. Be compatible with at least Windows, Mac and Linux.
3. Be relatively mature.
4. Be under a license that does not require Copyright text in the documentation of derivative works distributed in compiled form. Examples of good licenses would be the Zlib/libpng license, the Boost software license and of course public domain. Unusable licenses include LGPL, BSD, MIT etc.

Does anyone have any tips?

Kind regards,

Philip Bennefall