Qt is a widely used development toolkit that allows you to run the software it creates in virtually any modern operating system. This feature is achieved by compiling for a certain operating system without making changes in the program code. The toolkit is designed for development in C++, but also supports "bindings" to other programming languages (PHP, Java, Ruby, Python).
Qt has become the basis for a huge number of projects, including those for the KDE environment. This toolkit contains all the main classes, including those used to create graphical shell elements, work with databases and network resources. In addition, the toolkit uses the Meta Object Compiler (MOC) source code preprocessing system, includes a WYSIWYG-supported interface modeling environment (Qt Designer), is able to work with plugins and widgets, and comes with detailed documentation.
Qt libraries are conveniently separated into components (QtOpenGL, QtSql, QtUiTools, and so on), making them very easy to use. The toolkit is available to everyone because it is completely free for non-commercial use (the GNU LGPL and GNU GPL licenses).