Multi Site Manager Addon1 user found helpful
I saw that ImpressPages CMS has come out with something like this:
Can any of the current multisite addons be extended to support this sort of thing?
We created a separate add-on to handle registeration and site creation for new user accounts, it was just subdomains under that page.
However, that will only work well if you don't allow your users to access dashboard and need to only have 1 user account / site. When it comes to group management, user management, etc. I think a centralized installation of concrete5 would actually be better solution. There's even a ready guide for that: