Android: When you install a custom ROM on your phone, it probably doesn't come with Google's suite of apps. OpenGApps helps make it easier to get all the apps you need quickly.
The Open GApps project has existed for a while, but you had to download it directly from its site. Now, the project has its own app on the Play Store. Simply install it on your phone and select "Install" from the slide out menu.
The app will then help you pick the Google apps package you need. It will detect which version of Android you're running and which architecture the apps need to be built for. This makes it super easy to get the right package every time.