Currently contao enables you to host multiple sites in one installation, but it does not clearly divide the content of these different websites. In the way this is implemented in the current version of contao, it can be hard to manage because all the different pages, articles, modules etc can end up to be quite overwhelming .

I think it would be a huge improvement to show an dropdown menu in the backend (replacing the heading "Backend modules" for example) enabling you to select the site that you wish to work on. If you select one of these sites the backend will only show pages, articles, modules etc. of that particular website. This would improve the way people work with contao and make it much easier to understand for new users.