Orbiter is a freeware space simulator coded by the British professor Dr. Martin Schweiger, having been in development since 2000. The Orbiter community usually receives two new releases of the program a year; the first is the yearly update with numerous changes, and then usually a patch or two is released a few months later to fix bugs and to introduce additional changes to the program.
Orbiter one of the most realistic space simulators ever released to the public, utilizing a very accurate and robust Newtonian physics model for in-game flight. Players can fly in the Space Shuttle or in more futuristic craft, dock with the International Space Station or program a flight to nearly all of the planets and many of the moons within the solar system. Many helpful MFD (multi-function display) programs come with Orbiter to help you maneuver through space, and they can be configured in a pre-startup game configuration window so that you may pick and choose which ones you wish to use in-game. You may also start a scenario or saved game from this pre-launch dialogue, or make numerous other changes to to the program.
All of these features are visually represented through a graphics engine which is able to keep up with the sophisticated physics system running in the background while still being able to produce intimidating sights - from small asteroids to the super massive planet Jupiter. The graphics engine can have its quality scaled in the aforementioned pre-startup game configuration window, so that it will run more easily on less robust systems.
Orbiter is also very flexible in terms of modifications. Several new ships, multi-function display programs and celestial bodies (including entire solar systems separate to our own) have been released thus far. You may also download super high-resolution textures for pre-existing planets, with upgrade packages increasing their resolution to as high as 32768 x 16384 for the more commonly visited bodies.