Today I released Gretty 1.4.0, which incorporates all changes from @saladinkzn fork, including support of Jetty 9.3.
Here is the release announcement: https://github.com/akhikhl/gretty/blob/master/RELEASE.md
Gretty documentation is available at: http://akhikhl.github.io/gretty-doc/
Full sources available at: https://github.com/akhikhl/gretty
Compiled artifacts are available via jcenter, maven-central and https://plugins.gradle.org.