The text discusses the use of Razor templating language in rendering emails using various open-source libraries such as RazorEngineCore, RazorLight, Statiq, and in-process ASP.NET Core. The author provides a comparison of these libraries, highlighting their strengths and weaknesses, and demonstrates how to render a simple email template using each library. The example uses SendGrid for sending the email. The discussion also touches on the importance of understanding how each library works and its limitations before choosing one for use in an application.