At the end of every professional development course that I teach I offer an option to get a certificate of completion. The certificate is designed with Google Slides. The certificate is distributed through Google Forms with the help of the Certify'em add-on. This combination of tools makes it easy to create a custom certificate and have it distributed on request to students. In the following videos I demonstrate how this combination of tools works.
How to design a certificate in Google Slides:
How to send certificates via Google Forms: