Online/Offline manager. Should be able to add user name and password in admin section. Users have a login page, to log available/busy/unavailable. Only available operators show on the page.
I have a script like this currently installed, but transferring it to my new server didn't work, and I can not recover files from my old server so it may be easier to just re-write a new program, or you may be able to modify what I currently have.
Payment via PAYPAL when project is complete.
Sounds like an easy webdevelopment task. Will use PHP with a MySQL backend. Will include installation on your server. Look forward to working with you Kind regards