Jetty is a lightweight servlet container, easy to embed within a java application, there is an easy to use jetty client also.
Netty is an asynchronous event-driven network application framework.
You can write your own servlet container or http client app with help of the Netty framework for example.
Edit:
Forgot to mention that Jetty 8 and Apache Tomcat 7 support servlet 3.0 spec, but netty doesn’t. Because it’s not a servlet container.