A recipe blogging platform.
Each recipe step is annotatable in Rap Genius-esque fashion.
Recipe says "bake for 30 minutes"? Add a timer so your cookies don't burn.
Want your recipe reader to know the best technique for grilling that steak? Attach a youtube video of a celebrity chef showing how it's done.
Rails backend RESTful API.
Post-sign-in, Yumblr is a single-page app with Backbone MVC handling AJAX requests back to rails.