The list displays friend's who are online via FBM, so go ahead and invite them all.
You can send them a link to our download page, copy and paste this link and send to your friends via email.
Yes, FBM is cross platform it will run on Windows (xp, Vista, Win7), Mac OSX, Linux.
You will need to logoff (right click the FBM icon in the taskbar), the next time you log in you will be able to log in as a different user.
FBM supports three visibility states: Only Friends: This state allows only your friends to see that you are online. Public: This state allows all people on FBM with their visibility state as "Public" to chat Invisible: Let's you see who is online without them seeing you