Tabzon is an online in-out board, one that's way smarter (and cooler) than anything you've got hanging in your lobby or break room.
All you do is sign up for a free Tabzon account, then invite co-workers to the party. The service provides a custom, easy-to-remember URL based on your company name -- something like widgetco.tabzon.com, for example. Here's a quick video showing Tabzon in action:
Each person who signs up for the "board" can easily change his/her status for all to see. Tabzon provides three basic status options ("Available," "Unavailable," and "Busy"), but you can add your own ("Out to lunch," for example) and make it a permanent part of the list by clicking Add Quick Click.
Tabizon also lets you modify the status of multiple users at a time -- great if you're, say, the sales manager and about to pull your sales team into a meeting. A few clicks and the rest of the office can see their status.
This is one ingenious little service. I only wish it didn't require an entire Web page; I'd love to see this as a Windows gadget or tiny desktop client. Either way, it'd be the perfect thing to keep running in an iPad configured as a second monitor.