Apache Tomcat is a web server written in 100% Pure Java.

Apache Tomcat 10.1.x is the current focus of development. It builds on
Tomcat 10.0.x and implements the Servlet 6.0, JSP 3.1, EL 5.0, WebSocket 2.1
and Authentication 3.0 specifications (the versions required by Jakarta EE 10
platform).