This project contains the binary font files served by Google Fonts: https://fonts.google.com
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.pb 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.
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 option is used with some of the fonts. If you modify those fonts, please take care of this important detail.