What kinds of calculators would people find useful?

[Andrey Shostak]

I know BiggerPockets already has a number of great calculators, but is there anything niche that people are interested in? Like a calculator to simulate this strategy (https://www.biggerpockets.com/forums/61/topics/795487-retire...), maybe showing how much equity could be pulled out of which property when, whether the portfolio would still cash flow, etc. Or a seller finance calculator showing the monthly payment based on negotiated price, interest rate, down payment, etc. A sub-to calculator showing how much cash a seller can avoid bringing to closing. Any other ideas?