The TeaServlet is a template engine that works with the Tea template language. The TeaServlet makes it easy for developers to create web applications that separate the data aquisition from the presentation. Jason Hunter highlights the benefits of using a template engine such as the TeaServlet in his "The Problems With JSP" article.
The TeaServlet is a standard servlet and will run in any servlet container that supports the Servlet API 2.1 or higher. This includes free servlet containers such as Tomcat and Resin or commercial servlet containers such as BEA Weblogic and IBM WebSphere.
The easiest way to get started with the TeaServlet is to read the Tutorial and the User Manual.
You can read more about Tea and the TeaServlet in Jason Hunter's Java Servlet Programming book.