I use https://noteplan.co - it integrates calendars, reminders and markdown notes.

Calendars and reminders use their respective MacOS system apps (those can be used with Exchange, CalDAV and CardDAV servers which is important to me). The note-taking part of the app has a lot of niceties (task management, subfolders, tags, wiki-style-links, attachments, ...) and is split into a general-purpose "notes" folder and a "daily notes" folder. If you open a daily note, you get a combined view of a markdown note for the day in the center, your calendars and reminders on the right and all your general-purpose-notes in a sidebar to the left. I find this combination so useful that Noteplan is the only app I (very grudgingly) a) pay a subscription fee for and b) sync via a commercial cloud service - in this case Apple's CloudKit.