I use this one myself: we like to take walks, and not always are the routes marked that clearly. Still only a handful of users, but usefull I guess for anyone that wished that e.g. Google maps made it possible to upload a picture to be laid upon the background map.
Earlier apps: 1 - the UNofficial Prezi Player app. Used in 56 countries, it relied upon a hack to be able to play a prezi on an Android phone or tablet. Was quite succesfull, untill of course Prezi made an official Android app of their own. (Actually: demonstrated it to Prezi and they asked nicely to make sure no one would think it was official)
2 - a ‘fixer’ of Prezi’s. This was in the time that Prezi’s could become ‘corrupt’ as one of the elements was to small such that the code would give a ‘divided by zero’ problem. I fixed a lot of these errors by hand, before I made a (paid) service, and before that a java program that fixed this by going into an XML file, finding the smallest item, and enlarging it. (Am very happy with Prezi by the way, was invited (but declined in the end) to join them for a hackathon in Budapest, was made their first ‘prezi champion of the month’, and they gifted me a life long licence for their software).
3 - I do have another app - LetsDoThis - but this one is different: it did not scratch one of my own itches, but that of my eldest daughter: she wanted to ‘swipe’ away choices like one can on Tinder. This app never really went of (my daughter did not come through on her promise to market it among her fellow students;-0
(Edit: added ‘1’ ‘2’ etc)