Cartes du Ciel is a freeplanetarium program for Linux, Mac OS X and Windows. With the change to version 3, Linux has been added as a target platform, licensing has changed from freeware to GPL and the project moved to a new website.
The software maps out and labels most of the constellations, planets, and objects you can see with a telescope. It can also download Digitized Sky Survey Charts and superimpose images over these charts. Numerous star charts and indexes can be installed. There are also telescope interfaces and many versatile display options.
According to the programmer, Patrick Chevalley, it was released as freeware because "I’d rather see amateurs spend their money for a new eyepiece than for astronomy software". Chevalley has also created a lunar atlas program, Virtual Moon Atlas, which is also free software.