Information on Updating from Selenium 1 to Selenium 2.
The Java and .NET versions of Selenium 2 provided implementations of the original Selenium API
The legacy Firefox Driver was developed as a browser extension by the Selenium Developers. Firefox updated their security model, so it no longer works. You now need to use geckodriver.
Selenium Grid 2 supported WebDriver and Selenium RC. It was replaced by Grid 3 which removed RC code. Grid 3 was completely rewritten for the new Grid 4.
Information for working with platform names in Grid 2.
Working with the Standalone Server.
Summary of additional constraints that arise when running Selenium2 in parallel.
How to work with Native Events in the Legacy Firefox extension.
Details on how Selenium 2 accepted untrusted SSL certificates
Describes how Selenium 2 supported Android and iOS before Appium was created
Items of interest for moving from Selenium 1 to Selenium 2
This is who you can blame for the Selenium 2 release.