You know this concept from your car driving lessons: You have your steering wheel and your pedals and mirrors and the instructor has got his own set (in most countries minus the steering wheel).
In our small-group training sessions, our students take turns and apply what they have learnt in front of the class: one set of screens to work, three more screens to follow along.
We need large mouse pointers with different colours for training: One for the trainee that is active, and a pointing-only mouse-pointer for the trainer. (Optionally the trainer could actively use his/her mouse and also click stuff, but the pointer should in this case change colour or give a visual feedback.)
So far we are already using two mice, and Windows can handle that just fine. But it is often confusing to the class, to follow who is doing what.
For those who love context: This is for complex and full screens, like when we train for desktop publishing with not-trivial documents. It takes a lot of time, for the teacher to orally explain what tool to grab and where to find certain hidden options. So pointing is more efficient than telling.
We do not limit our search to free or open source tools, we could spend some money for such a tool, because we only need very few licences. If there were a similar tool for Linux, especially OpenSuse, we would also love to hear about it, but that is optional too.