Protractor and Selenium both are used to automate front end of web based applications. Generally most of the people are well aware of Selenium ( Java and Python bindings) and afraid of choosing any other tool on top of Selenium. I will compare Selenium and Protractor in this post, which will help you to decide which tool is best suited for your requirement.
Official website of Selenium says that:- Selenium automates browser. It does not specify any specific technology based web applications. Selenium can be used to automate any technology based application which needs a browser.
Official website of Protractor says that:- Protractor is an end-to-end test framework for Angular and AngularJS applications. Protractor is designed specially for automating Angular applications. Although Protractor can be used for any non-angular application as well but the beauty of Protractor for Angular application will be missed.
For detailed comparison, refer Protractor vs Selenium