Doesn't a product like GAT force you to push an extension to users. This extension is then able to read what the user has as extensions.
Also as for Apps, maybe you can go into the admin panel, Security and API Permissions ( at the bottom Installed Apps). and see applications used and users numbers. No way to export this but you can copy and paste to a spreadsheet. Could be very big for a list.
example
Take the part before.apps
450232826690-0rbs9d2fps9tifvk2oodh3tasd7vl7
Open reports>Audit
Choose Tokens
Filter on client id
Put in 450232826690-0rbs9d2fps9tifvk2oodh3tasd7vl7
This will show the user of that application
Not a pretty approach but depending on how you allow apps that could be feasible.
Extensions I think will require an addon of another extension...LOL
Please feel free to correct me on that thought.