The financial advise tends to be to pay off your smallest debt first, even if the interest is low, because it will give a mental boost...
So yeah the website would ask you to list your debts in order. (Student loan, car loan,...) And the interest rate.
Than it would make a (not too depressing) visual and ask you how much you can pay per month.
Bonus points for using Google sheets as a backend.
But main thing would be that people would be able to get helpful reminders / tips.
"You've saved yourself 500$ over the next 10 years, keep up the good work".
Christmas time "If you got a Xmas bonus and can double your loan pay off this month you'll speed up your debt freeness by 2.5 months"
"Did you know:A Starbucks frappucino cost 0.55c to make, and in ventti size costs 8$ and 400kcals (more than 2 ice creams). The coffee of the day cost 0.40c to make and cost 3$ and 10kcal. Caffeine the same.
Anyway v 0.1 probably only takes a day to make.
Cool initiative good luck