Stellarium

Celestia   (Compare Project)

Mostly written in C++

License: GNU-GPLv2

Gravit   (Compare Project)

Mostly written in C

License: lgpl

Gaia Sky   (Compare Project)

Mostly written in Java

License: gpl3

Nightshade Astronomy Simulator   (Compare Project)

License: gpl3_or_later

Aciqra   (Compare Project)

Mostly written in C

License: al

KStars   (Compare Project)

Mostly written in C++

License: gpl

Sky Chart / Cartes du Ciel   (Compare Project)

Mostly written in Pascal

License: GPL2

PreviSat   (Compare Project)

Mostly written in C++

License: gpl3

Functy   (Compare Project)

Mostly written in C

License: mit

Step   (Compare Project)

Mostly written in C++

License: gpl