Here you can find the release notes regarding RadEditor for ASP.NET AJAX http://www.telerik.com/products/aspnet-ajax/whats-new/release-history/q2-2010-sp2-version-2010-2-929.aspx
and in the RadEditorMOSS_5_8_6_Dev.zip package there is a readme.txt file, where you can see the MOSS related features. For you convenience I attached it to this thread.
All the best,
the Telerik team
Registration for Q1 2011 What’s New Webinar Week is now open. Mark your calendar for the week starting March 21st and book your seat
for a walk through all the exciting stuff we ship with the new release!