Startup Idea: Cross-Platform Personal Assistant Calendar App

Startup idea to develop a robust personal assistant calendar app that is user-friendly, operates across all technology platforms (PC, Mac, tablets, smartphones, smart TVs, smart cars, etc.), includes customizable privacy and sharing features, and supports multimedia like links, videos, audio, photos, etc.

I am a freelance personal assistant. One of my biggest issues is finding calendar software/apps that are user friendly, work across all the device options I have to work with (pc's, macs, tablets, smartphones, smart tvs, firetv/roku type devices, smart cars, etc), has privacy and sharing functions that can be customized, and that can handle things like holding links, videos, audio, photos and the like. I would most definitely pay for this software. I have been looking to buy this software for over a year.