I built Rocket League Replays[1], a website which analyses the replay files generated from matches played in Rocket League. I took my inspiration from GGTracker[2] which is essentially the same thing, but for StarCraft 2. I was looking through the replay files and noticed that there was some human readable content in them, so I wrote a parser[3] and built the site around it. Eventually I started a Patreon which allowed users to support the site in return for more advanced analysis. I get around $200/mo from that which covers the server costs etc, so I'm more than happy with that.
[1]: https://www.rocketleaguereplays.com/replays/
[2]: http://ggtracker.com/landing_tour
[3]: http://danielsamuels.co.uk/words/2015/07/27/rocket-league-re...