Cool. However, what I really want is an app that trains me while I'm doing my own work. Going to a specific site to practice on that site is great and all but it doesn't help me remember a shortcut nearly as much as learning that shortcut while working on my own work. Learning on my own work is far more likely to be retained, because my brain can link the recently learned shortcut with something which has meaning to me and is likely to be far more top of mind than a random lesson example.
Shortcat seems like a great complement to shortcutFoo! Very cool idea.
(disclaimer: I created shortcutFoo)