Hi Ashwani,
CCM or now called RHEA is different from OpenACS CMS. Although both have little tutorial. RHEA does have a slightly better UI, but the functionality is similar. There CMS do have a similar looking data model, but upon looking at it deeper they are actually very different. RHEA and OACS core data model is similar.
In OpenACS the CMS heart is Content Repository (CR) and other applications such as file storage, bug tracket, etc. make use of CR. In RHEA currently only CMS makes use of the CMS data model.
You can look at this post for the difference in OpenACS and RHEA data model.
https://listman.redhat.com/pipermail/redhat-ccm-list/2003-February/000791.html
Hope this puts some introduction to the difference and similarities of OpenACS and RHEA.
