Gave it a quick spin, it looks potentially useful. The mortgage calculator seems way off though; I put in some toy numbers ($1m 30yr fixed mortgage @ 3%, copying in values from the external calculator that's linked) and it's computing the payoff in about 5-6 years instead of 30. Ideally you could enter the mortgage terms like period, APR, and have the calculator back in to the mortgage payment, since the monthly payment is more of an output rather than an input in mortgage planning calculations.

Mortgage details are likely to be the dominant term for homeowners, so seems like this one would be important to fix. Plus mortgage interest compounding calculations are pretty opaque to most people, so it would help with explaining different structures (e.g. ARM vs. fixed vs interest-only, what portion of your payment is going to principal vs. interest over time, etc.).