This is great, I've seen a web game that you can use to practice vim schortcuts. But since this one's about building muscle memory, I don't see how this is going to be better than the actual use of the editor itself. Using the actual editor not only gives you the actual feeling but also challenge you with the real text editing tasks. CMIIW. But this is still useful if you just want to see a cheatsheet or not knowing certain shortcuts in the editor.