I like to wander around the cities quite a lot (still intermediate compared to others, but putting about ~10km/day for the past few years), and over the holidays, we were chatting with my friends about "places we've covered around the world together", it prompted the idea to have a co-op world tracker, with sides of city exploration. Built this iOS app - https://apps.apple.com/us/app/ato-discover-compete/id6757285.... Works with Apple Workouts + Photos location data. Just a headsup, the data is stored in my servers, so it's not a local app, since my goal was to get a combined data with my friends' data.
In my old app, I was solely tracking the streets, but it became somewhat impossible to have pretty coverage after I moved cities. And it's more fun to see global coverage anyways. Over the past couple of years, I've been getting emails for similar features that would expose city/country wide stats as well. Going to share with the users of the old app once I port its features on this one.
Still actively polishing it over the weekends, but it's very fun to see all the places I've been to on a hex-based map, combine it with my friends' data, and so on. It's been a very fun project so far.