Qt is free for development of free software on the X Window System. Qt also supports Windows 95 and NT, with native look and feel. Qt is currently used in hundreds of software development projects world wide. Qt dramatically cuts down on development time and complexity in writing user interface software for the X Window System. Qt is fully object-oriented.
Reusable components can work together without any knowledge of each other, and in a type-safe way.
Qt has a very fast paint engine, in some cases ten times faster than other toolkits. The X version is based directly on Xlib and uses neither Motif nor X Intrinsics. Note that the toolkit is the same, only the licenses differ.