Not very home cooked, but once I was working on a project/startup of mine that involved tracking degrees of freedom/trajectories and it was very manual/empirical testing, so I made a second app that would plot everything for me in real time, receiving data via socket. This was before iOS had any AR frameworks and just as Metal was released. Nothing existed to test AR, so I made it myself, with my data format, exactly like I wanted it and it was such a quality of life feature.