Screen Leap. Screen Leap is a site that allows you to share your screen with someone so that they can follow along with your mouse movements and clicks. The best part about Screen Leap is that there is nothing to install and no account sign-up. This makes it very simple to use and extremely fast. For the person on the other end of the "tutorial" you can share a special code and they can vist the Screen Leap site and enter it to see your screen (no limit on the number of people who view it).
When I taught computers, I used join.me to share my screen with my class when I wanted to show them something in a pinch. The issue with join.me is that as the presenter you have to download a file in order for it to work. However, join.me also offers an iOS app which makes it very handy for use on the go.