Autodesk Maya 2011 was developed using Qt by Nokia. Qt is a cross-platform application and UI framework and can be used to create plug-ins for Maya 2011. Learn more about Qt.
If you are looking to download the Qt SDK including Qt Designer for developing for Maya 2011, you can get your download here.
To get started developing with Qt, please download the appropriate
package. Maya 2011 is based on Qt 4.5.3. The links on the right-hand
side of the page point to the appropriate version.