Content repository is now independent from Sites. One content repository can belongs to multiple websites. When creating a new website, you are allowed to use an existing content database by inputing the name of that database or create a new one. The content inheritance concept has been replaced by content broadcasting. You can enable the content broadcasting feature under database settings. When enabled, you will be able to define content broadcasting sending and receiving rules to send content to or receive content from other websites.

The Text schema from V2 has been renamed to: Content type. We do not have binary schema any more. If needed, we have a new media library to store multi media files or you can store binary files in a text content.

In V3, all the content management pages are template based which means that you are able to modify the content list page, conent edit page or the category selection windows yourself. You can enable this "Custom Template" feature in the Database setting and change them in the content type editing screen.

Unfortunately, there is not a migration tool, you have to do this database migration manually.