We currently use teamviewer / join.me for many remote users to share their screens in a collaborative teaching environment. Usually, one instructor monitors half a dozen to a dozen students. We've found skype and google hangouts to be unreliable in the past. Gotomeeting, unfortunately, only supports a 1 to many screen share (not many to one or many to many).
Unfortunately, join.me occasionally has hiccups as well. VNC is too difficult to set up for our students due to home NAT setups. Is there an alternative that we can run dozens of in parallel? We do not need remote control, so in theory we could engineer our own solution. We're comfortable setting up a server if it buys us reliable and fast screen sharing.