I've been working on a fitness app for weightlifters and I finally finished it earlier this week. You take a video of yourself doing a lift, then the app gives you the bar path and velocity so you can analyze and improve your lifts. Here's what it looks like
Check it out here
I also wrote a blog post about how I troubleshoot my squat using the app

Check it out here
I also wrote a blog post about how I troubleshoot my squat using the app