Unfortunately, these tools are not free. I have found that spending that little amount out of my pocket has been worth it, for the amount of times I have used it, with students in class, as well as with teachers in PD workshops.
Here are two different versions of a spotlight for each operating system. (Sorry, there is nothing that I know of that works with Chromebooks, yet.)
Mac: Mouselight $0.99
PC: Pointerfocus.com $9.95 (You'll get a free 10 minute trial to test it out)