There are only a few Add-ons that are deployed globally on our sandbox, all of them are by Jive. When you deploy add-ons on our sandbox (https://sandbox.jiveon.com), you are the only one who can see that Add-On and any of it's contributions to the platform.
Update: There were a few that had accidentally been installed globally. I've since removed them down to the minimum set. Hope that helps a bit.
Thanks Ryan Rutan !
I agree, that I only can see the add-on on Sandbox.