Most people today use calendar applications like Google Calendar in order to sync up their days. While this solution helps maintain organization from a mobile perspective, there are also many times when it would be beneficial - both at work and at home - to have those calendar applications sync to an actual calendar, much like one that would hang upon the wall in your house.
From this arises the idea to create a digital "sign" or calendar-like display that could hang on any wall in your home. The calendar would easily sync to any cloud-based calendar application you already use, and it would be able to read/write in both directions. For example: if I'm sitting at home looking at my calendar on my wall, I could tap on a day (brining up a keyboard, much like what would happen on a tablet), insert some information or event reminder, and then have it automatically sync to my phone's calendar. Similarly, if I make some arrangement while at work on my phone, my wife or kids could easily see that I've made a new appointment. There are obviously countless cases where this might be beneficial.
Monetization could be as simple as just charging for the display, but it could also grow to become connected to the Internet of Things. Have an anniversary date planned with your wife? Maybe the calendar will give you gift suggestions on what you could purchase for her. Kids birthday next week? Enter some of your child's interests and maybe the calendar will give you great deals on a new game, discounted party rates at a movie theatre, etc.
This idea can obviously be expanded upon greatly, but as a concept it is strong and has definite market potential.