Just for the hell of it, I calculated RPI ratings for the FBS for the 2019 season.
Now it doesn't work exactly the way it does in basketball or baseball, though.
You can think of the usual RPI as giving each team 1 point for a win and a 0 points for a loss and then averaging each team's number of points over each game, and using those averages and those of opponents and opponent's opponents to come up with rankings.
In this system, I replace the 0s and 1s with the actual point differentials from the games (because not all wins and loses are the same, right?).
Here's the rankings 1-130:
Kinda surprising Ohio State is number 1, but they were #1 at the end of the season in some rankings systems (like Bill Connelly's).
The other big anomaly is FAU being the top G5 team.