While developing my own application server I've discovered several other wonderful examples of this kind of applications.
Lets not wait anymore, my favorite is so far Apache Tomcat. It has a nice modular architecture that provides you with the ability to develop new interfaces, it already has AJP and HTTP implemented, but you could just implement what ever you wanted, thats nice.
The configuration is straightforward and the community is good(I've tried the IRC, a bit slow, but really good).
I won't go into examples, because I have not yet developed one. But be assured that this is a good product, can't wait till the new version comes out(v7)
Next up, is another geeky post, about my adventure with LFS.