Systems Tool Kit Alternatives

Stellarium is a free open source planetarium for your computer. It shows a realistic sky in 3D, just like what you see with the naked eye, binoculars or a telescope.

Celestia is an application for real-time 3D visualization of space, with a detailed model of the solar system, over 100,000 stars, more than 10,000 galaxies, and an extension mechanism for adding more objects.

Space Engine - a real-time 3D space simulator, procedural universe generator and visualiser. It lets you explore the universe in three dimensions, starting from planet Earth to the most distant galaxies.

Universe Sandbox is an interactive space simulator for Windows based PCs.

Gaia Sky is a real-time, 3D, astronomy visualisation software that runs on Windows, Linux and OS X.

Cosmonium is a 3D astronomy and space exploration program. With Cosmonium you can navigate in our solar system and discover all the planets and their moons.

Orbiter is a realistic 3D real-time space flight simulator program.

3D simulation of the Solar System and night sky - real time virtual orrery and observatory

Mitaka is software for visualizing the known Universe with up-to-date observational data and theoretical models. Mitaka users can seamlessly navigate through space, from the Earth to the edges of the known Universe.

Engage in space exploration and terraform new worlds in this fun and exciting planet building simulator rooted in real science. TerraGenesis dynamically animates entire planets with changing biospheres, all based on real data from NASA.