The obvious answer is to use screencast software. These all require a network connection.
Screencasting is actually a small part of a larger industry which includes all video conferencing software\hardware. You will find that most of these products will also do what you need.
Another possibility is to use VNC software for this (this link mixes them in with RDP software so be careful to choose the correct items). These programs aren't specifically meant for this purpose though and may waste a lot of resources. These will also require a network connection.
Without using the network you have a few options which I can think of:
Use the projector which you've already said that you don't want.
You could use a large TV instead of a projector (which may be cheating a little since this is basically the same thing; the main difference is that this won't wash out in high light conditions).
This concept could be extended even further by using a specialty device (read this as meaning VERY expensive) which converts your digital output to RF (meaning that you could tune into a channel on your TV and pick up the output as a standard TV station).
My last option is to use a video camera to record your screen which will then be able to use one of the other methods to transmit back to individual computers. This is really not much different than the other options after that point but if you cannot add software to your computer (and do not have a large display) then this may be the only option for you.