Selenium is a open-source and portable software testing framework for web applications. Selenium provides a record/playback tool for authoring tests without learning a test scripting language (Selenium IDE). It also provides a test domain-specific language (Selenese) to write tests in a number of popular programming languages, including Java, C#, Groovy, Perl, PHP, Python and Ruby.
Now talking about the companies who are using Selenium are as follows. Apart from Salesforce, companies like ThoughtWorks, Google, Mozilla, LinkedIn use Selenium. If you also want to make your career in the testing field then you must have a look at the following Selenium Training Course. If you like reading you must read the following Selenium Tutorial. You can also refer to the below-mentioned Selenium video tutorial to learn Selenium. .