My friend created an app for digitally leaving comments, wasn't created with tourism in mind but it meets at least some of your criteria: https://itunes.apple.c

My friend created an app for digitally leaving comments, wasn't created with tourism in mind but it meets at least some of your criteria: https://itunes.apple.com/us/app/footmarkz/id715107924?mt=8 https://itunes.apple.com/us/app/footmarkz/id715107924?mt=8