> Pretty much anything you'd like to do with CouchDB or MongoDB
Wekan is a Trello clone that uses MongoDB for storage. On Sandstorm, each board lives in a grain, so there ends up being one MongoDB per board. This works fine. The only thing stand-alone Wekan ever did that queried multiple boards at once is display the user's list of all boards. On Sandstorm, displaying the user's grain list is Sandstorm's job, not Wekan's -- and indeed, usually the user is more interested in seeing the list of all their grains rather than just the Wekan boards, so delegating this to Sandstorm is a UX win.
If that is not the kind of example you have in mind, then you really need to give a specific example.
Wekan is a Trello clone that uses MongoDB for storage. On Sandstorm, each board lives in a grain, so there ends up being one MongoDB per board. This works fine. The only thing stand-alone Wekan ever did that queried multiple boards at once is display the user's list of all boards. On Sandstorm, displaying the user's grain list is Sandstorm's job, not Wekan's -- and indeed, usually the user is more interested in seeing the list of all their grains rather than just the Wekan boards, so delegating this to Sandstorm is a UX win.
If that is not the kind of example you have in mind, then you really need to give a specific example.