I've always found Productivity Apps ✨ cool ✨. Nice-looking Apps for Todos and Notes, as a single source of truth for everything going on in my life. But I learned that I don't work like that. Those Apps always felt wrong. I'm very organized without them. For some reason, I'm still envious of people when they show how they use some App to organize their life, but I don't try them out anymore.
I mainly use Emails, my Desktop, Calendar, and Post-It's. I know it sounds ridiculously oldschool, but it works pretty well for me. Let me explain:
Everything in my Email Inbox is something I need to do, and when it's done, the Email is archived. Some Emails only need a reply, and for other Emails I need to do something before I can reply. Some Emails can stay in my Inbox for weeks, until I can finally respond and archive them. Even when it's an ongoing task or discussion: as soon as I cannot actively do something and I need to wait for a reply, it's going to the archive.
This is what I use most of the time. When an online service can send me Email Notifications for things I need to act on, I'll usually activate them – for example GitHub Pull Request Reviews. Sometimes I also send mails to myself.
Similar to how I use Emails, but for longer-running tasks. For example doing taxes, invoices, contracts, collecting documents before I can send them off. I'll just put them on my Desktop until it's finished and can be sent off via Email or moved to my Google Drive. My goal is to keep my desktop clean. This often plays together with my Emails where I need to collect documents before I can reply.
For physical documents, I'll scan them and put them on my Desktop.
Easy, just to remind me of my schedule, with the addition that I also use it as task reminder when something needs to be done in a timeframe. For example driving my car to the garage before noon is a calendar event from 8:00 - 12:00. Booking train tickets can be a calendar event spanning a few days.
This plays together with my Emails and Desktop: When I buy concert tickets, I download them to my desktop, create a calendar event, and attach them. For business travels, when someone sends me train tickets and a hotel booking, I'll create a calendar event and attach it.
Smaller things don't fit into the above categories. When I want to remind myself of a task which needs to be done in a few hours or tomorrow, I'll write it on a sticky note and stick it onto my desk. It often happens during meetings or Slack messages.
Now that I finally wrote this down and thought a little bit more about it, I noticed that all of those places have one thing in common: they make me feel uncomfortable. I don't like Emails in my Inbox, files on my desktop, notes on my desk, or events in my calendar. With each day, the discomfort increases to finally "clean up".
Nobody likes doing tedious tasks, and for me, a fancy app contradicts too much with the burden of finishing those tasks. I would feel less of a necessity to actually do them. Maybe this reasoning sounds crazy, like I'm a huge fan of feeling uncomfortable. It's not that bad. I can relax even when I have some Emails in my Inbox. But I feel even better when they're finally done.