Hello Andrew Ryan,
Thank you for using our services.
I think that this is achievable. For each registered user you can create a page in Sitefinity for example. Then you can associate this page with a sub-domain on your website. Then each user will have access to their page only (and subpages they add to this page). And when logged in the backend they will be seeing only their pages. For this you can take e look at Domain-Page Mapping
. However the problem here would be permissions - i.e. separating each user which events will be able to create/edit/delete. Since Sitefinity 3.x does not support permissions on content item level (Sitefinity 4.0 will however) it means that all users from the same application will have access to all events from this application.
However the other option with having their own instances is achievable, as they will work with their own application and will be able to work with their own events.
I hope that this answer will help you. If you have more questions, please feel free to contact us.
the Telerik team