Some time ago Google, the company behind Android, introduced its very own app launcher among the many others already present with the name Google Now launcher. The launcher had no fancy features, just a basic app launcher with a Google Now pane integrated into it, hence the name Google Now launcher. But with the Google Pixel, and its own dedicated Pixel Launcher, Google now has two launchers on the Playstore.
But if an email obtained by Android Police is to be believed, Google is planning on discontinuing the Google Now Launcher by the end of Q1 2017. Apart from the different ways to access the app drawer, both the Google Now launcher and the Pixel launcher are almost exactly same. The only difference being that the Pixel launcher is not compatible (officially) with anything that's not a Google Pixel.
The email (below) says that the Search Launcher Services library for OEMs is now available. It has been in testing for a while now and Sony is probably the only manufacturer that has been playing around with them with many beta versions of its own launcher. What these basically mean is OEMs can now integrate Google Now into their stock launchers as a side pane just as it was in the Google Now launcher. As for OEMs that have been shipping devices with the Google Now launcher, such as Motorola, they can use Launcher3 from AOSP and just integrate Google Now using the Search Launcher Services library.
Google will stop approving new devices that try to ship with Google Now launcher starting March 1st however existing devices can continue using the launcher. If you install Google Now launcher now, or already have, you can continue to use it and it will be updated via the Google App but the Playstore listing won't be available. This could mean that Google plans to expand its Pixel Launcher to other devices but again, don't hold your breath on it.
Although, if you switch devices after the launcher has been discontinued. you'll need to find new options. Or you could just use the APK if you're that persistent.