Marble is a virtual globe application which allows the user to choose among the Earth, the Moon, Venus, Mars and other planets to display as a 3-D model. It is free software under the terms of the GNU LGPL, developed by KDE for use on personal computers and smart phones. It is written in C++ and uses Qt 4 or 5.Marble is intended to be very flexible; beyond its cross-platform design, the core components can easily be integrated into other programs.