ScreenStream lets others 'watch' your screen while you work.
It can be used as the modern equivalent of the overhead projector.
When you run this program on your computer anyone else on your network (or even the internet) can view what is on your screen by typing the link (and optional access code) into their internet browser. They can continue to watch your screen until you close the program.
It is also supports optional streaming audio so others can hear what you are saying.