Stellarium is a free "planetarium" program for your computer that allows you to look at the night sky at any given hour, at any given place in the world, at any given time rate, and point out the moon, constellations, planets, and major objects visible to the naked eye and binoculars. Slick, simple, and plain pretty to look at.
What I Use
There are plenty of articles out there about “must-have apps” and others that evaluate “here are all the programs that do this.” This is not one of them. Instead, this is a tour of the tools I currently use that didn’t come with my Mac, and why. I’m ignoring the built-in apps like the Terminal for command-line access or Disk Utility because if I don’t mention a third-party alternative, I’m currently using it, and you can check it out for yourself. Along the way I’ll mention a few good alternatives that didn’t quite fit my needs.