As a collaboration tool: our office whiteboard. I lost a bet with my business partners over it too.
I'm the young tech guy in the office and when we were setting up the new location this summer, I told the management team that we didn't need a whiteboard. Instead, I needed a TV and a computer, insisting that the whiteboard would never get used.
I bet them that the whiteboard would be a waste of money and that it would just end up sitting idle. Pen and paper as well as a functional screen and computer would be far superior, I insisted.
By the second month, it was clear how wrong I was and found it so much easier to get ideas across using the whiteboard to draw out diagrams over trying to get the right collaboration tech up on the TV screen. Having everyone in the room looking at a large whiteboard was also much more convenient than spinning my paper-pad around to show people sketches.
I accepted my defeat, bought my business partners lunch, and lost the whiteboard argument for good.