I'm quite intrigued by Glassboard. The privacy model looks great, and there are probably many ways that they can get good revenue. The big problem: they assume that everyone only wants to use the product on mobile devices, not on laptops and desktops. That seemed like an oversight, so I looked at their FAQ to see when other OSs would be added. The fact that Windows and Mac OS are not even mentioned seems kind of dubious, to say the least.