Qt is a cross-platform and open-source GUI (Graphical User Interface) toolkit for the GNU/Linux, Microsoft Windows and Mac OS X operating systems, and the next major update, Qt 5.6, promises to bring a huge number of fixes and improvements in almost all of the areas. However, the number one feature for Qt 5.6 is long-term support (LTS), which means that the software will receive updates and patch-level releases during the next three years.