Windows/Mac/Linux: Whether you're a die-hard astronomy buff or someone who'd just like an idea of what constellations are where, Stellarium is a fantastic tool for viewing the night sky from the comfort of your home.
At its most basic, Stellarium will display the night sky as seen from anywhere on earth. Delving into the more advanced features you can do all sorts of really interesting things like see the constellations for a dozen different cultures—the Pegasus from Greek mythology is the Turtle in the Navajo tradition.
You can watch the rotation of the stars in real time, control atmospheric conditions, zoom as though using a powerful telescope, and super impose a wealth of information onto the night sky like the names of stars, orbits of planets, illustrations of the constellations.
If you're using Stellarium on your laptop to supplement your stargazing, you can turn on a night mode that dims the brightness and displays the menus in a night-vision-preserving red. Stellarium is an open-source tool capable of displaying 210 million stars, and is available for Linux, Mac, and Windows.