I think it's a great idea. I've often toyed with the idea of something similar to use in-house and eventually turn into an application. It would be more geared toward transaction management for realtors and project management for investors.In a list format that you'd check off items based on some general pre-sets, which you could add to. Basically what I now do in Excel, but automated to a functional timeline.
Once completed the list would then pre-populate to a calendar and basically have user and/or system defined alerts, which could of course be modified by user. In a perfect world you'd agree to partner with the big box stores or maybe even Angie's List ( for contractors and for advertisements), to monetize the application.
Based on what task you've selected you'd receive offers for contractors, Home Depot/Lowes discounts, various coupons, etc. or you could pay a small fee and not have the ads and just use the app for transaction/project management.