COKE, PEPSI & DR PEPPER: It's happening: we're seeing different versions of a similar idea. Entrepreneurs know that competition "validates" a market. Even better: different approaches involve different tradeoffs, giving customers more fine-grain choices. That why we love watching the creation of tools for helping teachers find, organize and use the plethora of digital content floating around on the web. Count off: There's Ednovo, which uses human teacher and algorithmic smarts to collect, tag and organize a huge amount of material. (It's a great first stop when someone is looking for a primer on, say, "acids.") There's Edmodo, a thriving social network, that encourages teachers to create and share virtual bookshelves of materials with colleagues and students. (Great if you're teaching that class on acids). Now along comes 19pencils, which aims to make it easy for teachers to collect materials and instantly share them with all 19pencil users. (It adds other classroom tools into the mix, too, such as quizzes and performance monitoring.) All are--at least for now--free, but have to prove that they will have the chutzpah (and the resources) to grow. Gotta love competition and differentiation--it's a great recipe for building better products.