Selenium automates browsers and run in multiple browsers and operating systems. It cant automate desktop based applications.

The latest version of selenium is 3.8.0.Now 4.0 is also available

In the beginning there used to be selenium ide(works on Mozilla ,it is not robust and does not generate reports or logs and is not good for large no of test cases) and selenium rc (used for dynamic scripting using some program language.and can generate some reports just like web driver )and grid(used for parallel testing on different machines).

Now grid 2 is available in market and now the latest version of grid available is grid 3. Web driver was also there along with rc and it was an entirely different tool.It could also make dynamic scripts ,generates reports logs ,runs on multiple machines and works on different programming languages like java ,ruby ,python etc. Earliest version of webdriver was 2.0 Version 2.53.0 was the final release for webdriver 2,it was really stable and still used by many companies and then webdriver 3 came up.

Download the latest of Web driver from the link http://www.seleniumhq.org/download/