Why is selenium known as suite of software tools and not just a software tool?

Selenium is in-fact collection of different tools. As far as different automation tools which are in parallel with Selenium is concerned, be it UFT, RFT, Silk Test etc. they are just a standalone tool, however Selenium is not a standalone tool but a collection of different tools. These tools serve different purpose depending upon the requirements. These tools have been added over the years to handle the drawbacks of previous versions and handle new requirements which were not catered in existing tools. Different tools which are part of selenium test suite are:

1. Selenium IDE
   
2. Selenium WebDriver
   
3. Selenium RC
   
4. Selenium Grid