WebDriver is an open source tool for automated testing of webapps across many browsers. It provides capabilities for navigating to web pages, user input, JavaScript execution, and more.  ChromeDriver is a standalone server which implements WebDriver's wire protocol for Chromium. ChromeDriver is available for Chrome on Android and Chrome on Desktop (Mac, Linux, Windows and ChromeOS).  

Latest Release: ChromeDriver 2.20

ChromeDriver Documentation

All code is currently in the open source Chromium project. This project is developed by members of the Chromium and WebDriver teams.