Fantasy Monday is my free, Monday only subset of Fantasy Math. It lets you put in you, your opponents score, and get back the probability you win (with some nice distribution plots).
It's pretty popular, especially during the first week of the season when there are two Monday night games and everyone's excited about the season. I've written before about Fantasy Math and how I'm not positive it has product-market fit, but Fantasy Monday definitely does. Unfortunately, the price is free.
This was actually one of the earliest applications of the model. Way back with Bayesian Fantasy Football, I used to run the matchups for my league every Monday and report back on the league messageboard. The rest of my league has an ambivalent attitiude about my model, but they liked these Monday night updates, and would ask for the probabilities if I hadn't gotten around to posting them.
(While innovative, the Bayesian model had issues, especially towards the tails. I still remember the night a guy in my league won even though the model predicted he had like a 1/100,000 chance to do so — a true Monday Night Miracle!)
Now, of course, my league can check out their probabilities every monday like everyone else at https://fantasymonday.com.
During 2020, when a few games got moved to Tuesday due to Covid, I put up a Tuesday night version at https://tuesdaynightmiracle.com. This was more of a marketing gimmick than anything else, but got enough signups to pay for the domain name.