http://jbt.github.io/markdown-editor/#HY+xcsQwCER7f8V2aZIr8kfIwhZzEngEOc/9fdB1sMPuPkgrGk/+crgNNmXczXKra1xSNNETLkM6zW9gM+1vSKCKX53eDlGXyiD8/lyUrkHzWe1WcJWw+di2vBbHNa1QSbPach+H7H89EAYZdEo6m93IPs+WIWcLFN4TIaN3652KTQp58Sd4UbG+ZJoO1lhk1Atn1ecJiZZRjJiUUjSKxdz5iKxf6s7+2P4B and here's someone who's done something similar, only it displays inside a 2-pane markdown editor. it is probably not difficult to imagine how this might become a collaborative editing environment, albeit one with the trait that it left no traces.