GTK+ is a highly usable, feature rich toolkit for creating graphical user interfaces which boasts cross platform compatibility and an easy to use API. GTK+ it is written in C, but has bindings to many other popular programming languages such as C+, Python, Perl and C# among others. GTK is licensed under the GNU LGPL 2.1 allowing development of both free and proprietary software with GTK+ without any license fees or royalties. See GTK for more information.

An IDE for a number of scripting and markup languages. Newly open-sourced and based upon ActiveState’s well-established IDE and code base.