This project contains the binary font files served by Google Fonts: http://www.google.com/fonts
The top level directories indicate the license of all files found within them. Subdirectories are named according to the family name of the fonts within.
Each family subdirectory contains the .ttf font files served by Google Fonts, plus a METADATA.json file with metadata for the family, and a DESCRIPTION.en_us.html with a description of the family in US English.
Also /designers contains a list of the Google+ pages for the fonts' designers.
You can download all Google Fonts in a simple ZIP snapshot (over 250Mb) from https://github.com/google/fonts/archive/master.zip
You can also sync the collection with git, so that you can update by only fetching what has changed. To learn how to use git, Github provides illustrated guides and a youtube channel, and a learning game that takes just 15 minutes. Free, open source git applications are available for Windows and Mac OS X.
It is important to always read the license for every font that you use. Each font family directory contains the appropriate license file for the fonts in that directory. The fonts files themselves also contain licensing and authorship metadata.
Most of the fonts in the collection use the SIL Open Font License, v1.1. Some fonts use the Apache 2 license. The Ubuntu fonts use the Ubuntu Font License v1.0.
The SIL Open Font License has an option for copyright holders to include a Reserved Font Name requirement, and this is option is used with some of the fonts. If you modify those fonts, please take care of this important detail.
Source files for each family are often available from the designer, or from https://github.com/googlefonts
These fonts are usually the result of collaborative projects, where you are invited to discuss issues with the designers and even contribute to their on-going development.
When customising or remixing fonts, please do contact the designers to understand what they might need in order to include your improvements.
Most of all: Enjoy the fonts!
– The Google Fonts team, 2015-06-18