What are some alternatives?
When comparing Sky Map and Gaia Sky, you can also consider the following products
Stellarium - Stellarium is a free open source planetarium for your computer.
KStars - KStars is a Desktop Planetarium for KDE.
Space Engine - Space Engine is a realistic virtual Universe you can explore on your computer.
Solar System Scope - 3D model of the Solar System and night sky in real time
SkyView - SkyView is powerful, easy-to-use app that answers questions about stars, constellations, and more.
Celestia - Celestia - real-time 3D visualization of space.