KStars is distributed with KDE as part of the kdeedu "Edutainment" module.
KStars is been packaged by many Linux/BSD distributions, including Fedora, openSUSE, Ubuntu, and Mandriva. Some distributions package KStars as a separate application, some just provide a kdeedu package, which includes KStars.
If you would like the latest Git development version of KStars, please follow these instructions.