wxWindows, found at http://www.wxwindows.org, is a cross platform GUI library. Its is mainly used as a library with C++, but has bindings to other programming languages such as Python, Perl and Ruby. It relies upon a systems 'native' windowing libraries so it gives you the LookAndFeel of that platform.

Its design is similar to that of MFC but much more consistent.

It is, of course, OpenSource and runs on Linux.

Which OpenSource? GPL so you can't use it in a commercial program? LGPL so you can't steal the library? BSD style?

"The wxWindows 2 licence is essentially the L-GPL (Library General Public Licence), with an exception stating that derived works in binary form may be distributed on the user's own terms. This is a solution that satisfies those who wish to produce GPL'ed software using wxWindows, and also those producing proprietary software."

"Richard [Stallman? has confirmed that the new licence is compatible with GPL'ed applications. However, there are no significant restrictions on proprietary applications."