A feature I'd love to see is should I refinance or not.

I've currently got a convoluted system of spreadsheets which I have to update every time I want to recheck against current rates. I'd basically like it to tell me in which scenarios it would make sense to refinance. I input things like amount of principle still outstanding, my current rate and term, how far I am into that loan, when I plan on selling, what the refi rate/term options are. The outputs I get are total cost (in fees and interest) by the prospective sale date, and total equity by the prospective sale date.

It is not necessarily in a lenders interest to give borrowers this information, since borrowers are trying to optimize based on paying the least amount possible.