Heart Mail

A Gmail, Google Calendar, and YouTube app for macOS and Windows, written by Joseph Marikle for personal use.

Mail shows your inbox as conversations, marks them read as you open them, and writes replies and forwards.
Calendar shows your calendars by month, week, or schedule, answers invitations, and reminds you of events.
Videos lists the live and upcoming streams of the YouTube channels you subscribe to, and can put them on your calendar.
It works with several Google accounts, and notifies you for all of them at once.

Heart Mail isn't sold or distributed. It's a personal project, used only with its developer's own Google accounts. It runs on your computer and gets your data straight from Google, with no server in between. The privacy policy covers what it uses and why.