Selenium is a programming tool used to automate the browser — simulating a real user by opening windows, going to URLs, clicking buttons, filling in forms, etc. Selenium is primarily used for test automation, but can also be used for other things.
It is also referred to as Selenium WebDriver, because there were two different projects (Selenium & WebDriver) which did similar things and eventually merged. Selenium uses the WebDriver protocol (a W3C standard now) to communicate over the network via a REST API. This allows for remote automation,
There are other tools associated with Selenium, including Selenium Grid — which enables remote execution of automation and Selenium IDE — which allows you to record and play back automated steps without writing code, and has (limited) ability to to export from Selenium IDE to code that can run independent.
Selenium IDE does not support multiple users, but scripts can be exported and shared from one user to another.
Selenium Grid allows for parallel remote execution of Selenium scripts, which allows multiple people (or tests) to execute tests at the same time.
The concept of “supporting multiple users” does not really make sense in terms of Selenium as an open source development tool or coding library.
It would be like saying:
“Does Microsoft Word support multiple users?” or
“Does the Java programming language support multiple users?”
In the case of Microsoft Word, every user that has the program can use it, but collaboration is (primarily) done outside of the tool. With proprietary software like Microsoft Word, each user may need a license to run their own copy of the application, but Selenium is open source, so does not require the purchase of any license to use.
And as a programming library, any number of users can reference Selenium in their own code and execute it. Users can run multiple automated tests (or other scripts) at once — if they write their program to run in parallel.
But in order to maximize parallel execution (for single or multiple users) you need to have a remote Selenium grid. There is an open source grid that anyone can deploy, but there are also commercial services the host Selenium Grid with additional tools at a cost. These companies include Sauce Labs, BrowserStack, LambdaTest, and Applitools. Each company has their own policy about multiple users, and of the ones I mentioned, they all support multiple users in their own way.
This post is based on a question asked on Quora at: https://www.quora.com/What-is-Selenium-Does-it-support-multiple-users