difference between thoughtworks and openqa selenium -

what difference between openqa.selenium , thoughtworks.selenium? how compatible each other?

there no class selenium in package openqa.selenium, there class webdriver. want use webelement in test, imports thoughtworks.selenium.selenium.

some tutorials use openqa.selenium, other thoughtworks.selenium, , confused.

• thoughtworks.selenium original selenium (aka selenium 1, or selenium-rc).
• openqa.selenium selenium 2 aka selenium webdriver.