I have been impressed by Google Docs. The applications are simple, which is to say they are not overloaded with features I don’t need or will never use (hear that, Microsoft?) but focus on those things that are useful. I’ve been particularly impressed by their Drawing application, which is among the finest I’ve used, far superior to Microsoft Paint, and even superior to some of the image editing tools that came as part of MacOS.
I use Google Docs for other things as well, including managing my list of story submissions, but whenever I need to create a diagram from scratch, I always start with Google Docs drawing application, and so far, I have not been disappointed.