Automated testing software is used to check whether or not products are safe to be released to the public. There are 100's of automated testing softwares out there but the best hast to be Selenium. Selenium is an open source ATS and was released first in 2004. It has been programmed and re-programmed millions of times for the desired output and hence makes it the most efficient ATS out there. It supports almost every programming language and operating system.
The only downside to Selenium is the fact that it requires training to use and is not user friendly. If you are looking for user friendly ATS the best has to be Katalon studio. Katalon studio is for beginners and unlike Selenium it supports mobile apps as well. It's built on the structure of Selenium so even experienced professionals can use it.