I've posted before, but https://beatyourbookie.app/ is what I've been working on for a while.
The website is for tracking betting lines and finding arbitrage and +EV bets across sports betting sites. I've been hooked on the idea that there are inefficiencies in sports betting markets that can be taken advantage of, especially in betting on live events and so this started as me just collecting minute by minute odds data from different sites and going from there.
I'm currently collecting all the data myself so my next step is creating a public API to allow other users to access the same sportsbook data that I'm currently using (https://sportsbookapi.com).