Do you mean 'sites' ?
It's in the admin guide, page 109 , it works quite well, but not everyone likes it.
Use the Sites page to create independent sites for different organizations or groups on a single server system. Each site’s workbooks, data, and user lists are isolated from those of other sites. As the system administrator, only you can see every site and perform actions such as creating sites, adding and removing users, and make system- wide changes.
i have seen those pages and find them quite thin in content - what does it mean that workbooks,data and user lists are isolated from other sites?
are those content items and metadata separated at the db level?
are different OS processes instantiated to work on different sites?
can a single site's data/config be exported or backed up by itself?
do multiple sites share a common set of data sources and/or data connections?
any clarification is quite welcome
Your 'All Users' will reside across the sites (for administration), and you can see which users available to 'This Site'. All you do (as admin) is to authorise which users you'd like to have access to which site. Users can participate several sites or just the site required.
The site contains just the projects/workbooks for the users who have access to that site.
The problem I see is that if one user is part of many sites they might get a little frustrated navigating / logging off to go and look at a workbook in another site, but I guess in a segregated organization the number of uses doing this should be few ( maybe the CEOs ), maybe there's a solution to this issue of re-logging.
The alternative is to use 'Project Permissions' , which may get out of hand if you have lots of users.