TestFlight is an interesting service that has been in closed beta for a little while now. What this service does is provide Android developers an area that makes it much more easy to run any sort of public beta for their application or game that they may be working on. Instead of having to put the beta version of your game on Google Play, or provide a self-hosted or cloud-based download and having people manually install your beta, TestFlight allows people to download and install a beta version of your game off the internet and onto their device.
