Today, Google made a lot of Chrome OS users very happy. The full suite of Android apps will officially be coming to Chrome OS soon, starting with a few select devices. Later this year, the Play Store will come to Chrome OS, which means users will be able to buy and install Android apps just like they do on their phones and tablets. Notably, this is distinct from downloading Android apps via the Chrome Web Store, which Google first started experimenting with in late 2014.
Starting in "early June", Android apps will only be available for a few select devices, including the Asus Chromebook Flip, the Chromebook Pixel (2015) and the Acer Chromebook R11. Veteran Chrome OS users will note that all of these devices have touchscreens, which means Google may be waiting to roll out an entire store of touch-centric apps to devices that can't fully use them. For the later release, Google has a much larger list of Chrome OS devices that will support Android apps here.
In the meantime, developers can optimise their apps to run on Chromebooks right now. For the layman, that means that while you may be able to install Android apps, some of them might not be ideal until developers eventually get around to making things work correctly. However, we've been playing around with Android apps on Chrome OS for a while now and for the most part they're pretty great as-is.
Bring Your Android App to Chromebooks [Android Developers Blog]