RM 2.4 is mainly for compatibility; ensuring that RM works smoothly with all the changes in the recently release Alfresco One 5.1, and 2.4.a targets 5.1.e. It’s an Early Access version, meaning that we’re still working on fixing the last few bugs.
This is the first version we’re releasing following the work we did last year to allow us to make some of the new features Enterprise only. This means that some of the features I previewed in September's Tech Talk Live will only appear in the Enterprise 2.4 version, but RM remains open source and the core of the module will always be available for free in our community release. As the Community amps are the core of the Enterprise version, RM Community now also benefits from exactly the same level of testing our Enterprise releases go through.
You may have noticed that our GitHub mirror is lacking recent activity. We’ve changed our version control systems in-house and have been too busy getting the release out to fix the mirroring. It's a priority for me to get that working, hopefully before 2.4.b comes out.