Google Books (not to be confused with Google Play Books) remains one of Google's oldest services that is still active today. For starters, it is pretty much a gigantic directory for searching books, magazines, and texts that Google has scanned throughout the years. With more than 40 million scanned books, it is a vast resource of knowledge stored within Google's servers. And often, if the book is available in the public domain, it will also give you the option to download it in both PDF and EPUB formats completely for free. Oddly, though, it is one of very few Google services that do not have an Android app available for download, and in turn, the service can only be accessed in a web format (and a pretty outdated web format at that, too). Enter Leafster.
Leafster is an unofficial app made by XDA Recognized Contributor StrangerWeather which uses the Google Books API in order to scour through the service's vast collection of knowledge and, whenever possible, display snippets, partial previews, and even download the file entirely. Leafster also looks aesthetically pleasing to use since it tries to follow Google's Material Theme guidelines whenever possible, adding a few twists of their own as well.
You can check it out on Google Play Store right now.
You can also check out the official forum thread in our forums to know more.