OmniPortal is an unrelated project. Though it has a lot in common with the CSK and GCN it does not use the CSK code base. In many ways OmniPortal is superior in base architecture to the CSK/GCN. Nick Berardi, the mind behind OmniPortal is a regular contributer to the GCN project and a regular poster here.
The GCN 1.1 is an updated CSK code base and was designed to upgrade CSK sites in place (the upgrade process is documented in the GCN docs here: http://www.gotcommunitynet.com/documentation.htm under the installation section).
The GCN is not an official "starter kit" since it doesn't meet the requirements of a starter kit, but it is recognized by the ASPInsiders and Microsoft ASP.NET teams as an "official" upgrade as you can get.
Stephen M. Redd
http://www.reddnet.net