I want to get information - like the number of monitors the client is using. I need access to system calls and I understand that since the browser is sandboxed, it can't execute sys calls.
What other options do I have to do this (other than the client installing an app on the desktop)?
I found that this can be done using extensions. Chrome allows for access to such information through its "activeTab", "tabs", and "system.display" permissions found here https://developer.chrome.com/extensions/declare_permissions.
In general, extensions allow the website to have more control over the visiting computer and access to data to/from it.