OffHook allows work groups on the same local network to monitor the phone status of other OffHook users.
With the click of a mouse, a user can communicate to other users that they are beginning a phone call. When the call is over, they can easily switch their status back to available.
Although designed for telephony, you could use OffHook to track any kind of on/off state. (Lunch, meetings, out-of-the-office, etc.)