Startup Idea: Universal Calendar Syncing App

Startup idea to develop an app which can compile all data from phone, Google calendar, and Microsoft calendar. The app would allow users to make events on any platform and have them updated and visible across all devices on one unified calendar.

My phone, my google calendar, and my Microsoft calendar are not synced together on my devises.

A great app for a computer and/or a phone would be to have an app that can compile all that data together so I can make events on my phone, at work, and get events from personal events all on one calendar. No I havent.