There are more than a few free and open source task management applications out there. They run at the command line, on your desktop, and even on the web. They are, as you might expect, of varying quality, and with a varying number of functions. But there's pretty much a task management tool for just about everyone's needs.
Since early 2020, I've been trying to use Nextcloud as my personal hub. One app I've been experimenting with (again) is Tasks. Which, as the name implies, is Nextcloud's todo list manager.
There are a myriad of note taking tools out there. And those tools cater to a variety of needs and to a variety of user bases. It isn't a stretch to say that there's a note taking application for just about everyone.
If you use Nextcloud, you have a more-than-serviceable option in the form of (wait for it!) Notes. It's worth a look if your note taking needs are simple and you want to work in plain text.
A calendar is more than just something that you use to mark off the days until the weekend. It's also a powerful tool for keeping organized and keeping track of your appointments and more. One of the apps built into Nextcloud is a calendar.
Nextcloud Calendar is easy to set up and use. It packs just enough features for most people. And, if your needs are fairly simple, it's a great alternative to the popular web-based calendar tools out there.
When it comes to managing your work, sometimes a task list isn't quite enough. Sometimes, you're working on something that's a bit more involved or complex and which requires a tool that's a bit more flexible and can give you an at-a-glance awareness of the status of your tasks.
One popular way to do that is with a kanban board. One of the most widely-used kanban board applications is Trello. But being good citizens of the FLOSS world, I hope you use something more open like WeKan or something similar.
If you use Nextcloud as a personal productivity hub, you can add a kanban board to your instance with an app called Deck. Let's take a look at Deck and how to use it.