Yes, there is one; I've seen it in action, but didn't write it down.

Yeah... we had one at school that projected the computer monitor up onto a screen... can't remember the name, but there should be many... Really a great way for teaching how to do something on the computer.

If you are looking to buy one, you can probably find a decent one online. Make sure it is compatible with your computer (ports and operating system) before you buy. The good ones are pricey...
The link is PC Mag top 10 for computer projectors.

i think you call it an overhead projector

It is an overhead projector. Our Pastor has it set up each Sunday for services. Great for those Bible scriptures he is using in his sermons. We use it to design and paint items for decorating for VBS. Also, used it to project a picture on the walls in the nursery and primary Sunday School rooms for wall murals.

We have an overhead projector, connected to our computer, in our church too which displays our whole service, so there is no need now for books! It leaves your hands free which is also good. Love Chris

Like rescuer said : take care before you buy, if you have a new pc it could be that it screen resolution is too high for the beamer !

Computer projectors are fantastic fun. One thing to note is that the more you pay for one, the brighter it tends to be. You need complete blackout to use the cheaper ones.
BTW "overhead projectors" are really a different animal - they are a simple optical system for projecting from a transparency. I remember thinking that these were wonderful 30 years ago!