So Many Downloads…

What download is for what? Here it comes:

Package What is it? When to need it When not
Selenium IDE Firefox plugin for playand-record I don’t use it
selenium-server-standalone.jar Acts as a server communicating with automation script and remote browsers
  • if you run your case in a remote machine
  • If you use Selenium Grid for parallel run
  • If you use htmlUnitDriver and old Firefox driver (Firefox 47 or earlier), regardless local or remote, since these 2 drivers are included in this package
if you are launching browser locally
Language Binding such as selenium-java.jar, selenium-ruby.jar… Acts as an interpreter between automation script and webdriver Always needed for your chosen language Never
(such as chromeDriver.exe
geckodriver.exe etc etc)
Acts as a server to communicate with our test script, basically is a client Needed for each browser
Since selenium standalone server includes firefox (pre-firefox 48) and htmlUnit already, no separate download is needed for these 2 drivers if you have selenium standalone server already

There are a long list of 3rd party plugins to make Selenium automation life easier, but this falls out of our topic and thus is skipped here.