It's hosted by Stephanie O'Neill, and has been going since the beginning of the year. The challenge description encourages participants to "join Stephanie as she gives you alphabetical photo prompts that will help you get some layouts done about YOU!" Every other week, Stephanie posts a prompt, based on a letter of the alphabet. They are currently on "M" - "M is for Me".
Scrapbook Graphics has a gallery dedicated to the layouts inspired by the Alphabet Shoot challenge - go there and let yourself be inspired!
Go ahead...scrap YOUR stories!