By default, Ninite installs most apps for all users on a machine. This is because most installers behave this way by default.
There are a exceptions though. The following apps only install for the current user:
Ninite Pro includes an /allusers switch you can use to force installation for all users on a machine. This feature only supports Chrome and Dropbox at the moment. We are working on adding support for other apps.
Here's an example command:
NinitePro.exe /select Chrome Dropbox Hulu Firefox /allusers
It will install Chrome and Dropbox for all users. Hulu will be installed for the current user only since /allusers does not support it yet. Firefox will be installed normally (which is for all users by default).
* Please note that Dropbox will only be installed for all users when Ninite does not detect any existing per-user Dropbox installations on the system.