There are some overlaps between Calendar and To-Do app so I reuse some components here. I took iOS Calendar for reference, well, I am a fan of iPhone, iOS is just within my reach everyday.

The tab bar of Overview is what I learned from Calendar app of macOS. Today owns the highest priority so it sits at left side. In my design, Today is the default view so user could catch a glimpse of schedule quickly. All-Day event will be pinned to top. Categories of events are marked as different colors. The scenario of multiple calendar are not included here.

So that's it.