Mamba application server (based on Simple)
Offside the mainstream Tomcat-world:
Mamba application server provides a standalone implementation of the Simple framework. It is designed as an easy to use, extendable HTTP server, similar to a conventional Servlet engine. However, unlike a Servlet engine, Mamba does not use the Java Servlet API to extend the functionality of the server, instead, Mamba uses another, comparable, component system.
Link: Mamba 1.1