The Eck App (iPhone, iPad and iPod touch)
Come on, who doesn't want to learn more about—and even make themselves look like—MLB legend, Hall of Famer and skilled baseball commentator Dennis Eckersly? I gotta have it!
The Eck App gives you access to an "Eckipedia" of Eckersly terms; a What the Eck section to test your knowledge of Eckisms, and an Eck Yourself feature to superimpose Eck "moss" on people, pets, whatever, in your photos.
OK, it might not be a "must have" app for everyone, and some people I showed it to didn't find the software as amusing as I do. But to that I say: Go Eck Yourself.