Clarify -- now in Public Beta -- is Mango Learning System's new product for communicating screen-based instructions quickly and easily. It's something like a successor to ScreenSteps (which history will show I'm a big fan of), but in the words of developer Greg Devore, "while ScreenSteps was aimed at documentation, Clarify is aimed at communication."
Clarify provides a simple set of tools for taking screenshots, adding annotations, writing descriptions and then sharing the final step-by-step instructions you create using the free screensteps.me service or by email. The tools are an evolution of what was found in ScreenSteps, and are both better looking and easier to use.
You can take delayed screenshots (for setting up a dropdown menu before snapping, for example) and you can repeat prior screenshot location and dimensions, which is great for documenting things like navigating web pages where the only changes are within the browser window. The annotation tools are robust but not overwhelming, and the text editing tools are more Cocoa-like and familiar than ScreenSteps'.
Sharing via ScreenSteps.me is free and provides a dead-simple way to get your communication to its destination. You can also deliver it by email, but using the service allows easy updates and export to plain HTML, styled HTML or just images as well.
If all of this sounds useful for you, grab the free public beta and give it a whirl. Final pricing is undetermined at the moment but will be less than ScreenSteps. While Clarify is in beta it's a great time to offer new suggestions and help out with the development of the final release!