Looking for calendar and tasks tools

Haven’t started building anything yet but decided it would be best to map out what I actually need to host. Trying to move out of Google/Apple apps and need the best tools to replace Google Calendar and tasks. I find I use these a lot to set reminders for budgets, due dates etc.

I have seen Nextcloud come up a bit but I was thinking of maybe using separate smaller apps that specialize in each task. I don’t think I would use a lot of the Nextcloud features.

Ideally I would love to start replacing a lot of the iPhone apps over time and just have alternatives to everything