Space Invaders is a well-known arcade game developed by Tomohiro Nishikado in the 70's. Throughout the years numerous spin-offs were designed including Classic Invaders, an entertaining game that brings you an old-school look, same rules as the ones from the original app, and plenty of challenging levels.
In this two-dimensional arcade game, your objective is to control a laser cannon by moving it to the left and right side of the screen and eliminate all descending aliens. The level is complete once all alien ships are destroyed. You have access to 3 lives per mission. The game is over once you lose all lives (you lose one life if the missile of an alien ship reaches your spacecraft).
This app keeps track of your highest scores, lets you toggle windowed or fullscreen mode, and gives you access to a comprehensive guide.
All in all, I enjoyed playing Space Invaders even though some missions were a bit difficult to complete.
So, if you're into playing arcade games with an old-school feel, you should definitely give this app a try. Plus, you don't have to pay a buck to use it on your Mac.