The "Global Telescope" is the best free astronomical program, which includes a wealth of cosmic objects and interactive educational content, including virtual interstellar travel, which is explained by astronomers and experts. It applies to schools, universities, and planetarium around the world. If you've never tried it and are interested in the universe and the stars, then it's worth downloading.
Although the global telescope has always been free, today Microsoft announces that the application is open source, which is good news and will make this already great application become better. Microsoft said today that millions of people rely on "global telescopes" (WWT) as exploratory research, teaching and public outreach. Now with the open source "Global Telescope" project, any individual or organization will be able to adapt and extend the function of the global telescope to meet any research or educational needs, continuously improve astronomical research, conduct formal and informal learning and public awareness.
Global Telescope Project Address: http://www.worldwidetelescope.org/Learn/