Quote from Sam Mcgee:
Why would you need more than that? It works on any computer I might use. You can edit the picture, add arrows etc in paint. If I get used to a program like snag it, I won't know what to do when I'm on another computer that doesn't have snag it.
They also have Portable SnagIt, so you can carry it around on a flash drive and use it on any computer without having to install anything