Here's a list of the most noteworthy things in the RAP 1.5 M4 milestone build which is available for download since December 16, 2011.
With this new protocol, it is now possible to develop alternative clients for RAP. The exact format is described in the RAP Protocol wiki page. Some details may still change until the release.
Since RAP 1.5 will be available together with Eclipse Juno, the target platform is now based on Eclipse 4.2 instead of 3.8. However, the RAP implementation of the Eclipse Workbench remains to be based on 3.x. But there are a couple of important changes in the target platform.
org.eclipse.jetty. Instead of two, Jetty now consists of seven bundles.
org.apache.felix.gogo.*) support it.
Please adapt your launch configurations to these changes as needed.
This list shows all bugs that have been fixed for this milestone build.
The above features are just the ones that are new since the last milestone build. Summaries for earlier builds: