I am a pretty big fan of Obsidian right now. Here are some notes on it:
Check it out here: https://obsidian.md/
It's available for just about any system the average person will use.
Your info is all kept in Markdown text files which means if Obsidian goes away, you lose nothing. You can also take it with you if you find another program you like better. You can also edit those files with any program and keep using Obsidian for core features you like. It provides a ton of functionality without any real limits or risks of data loss or obsolescence.
The program itself is free but it doesn't come with any sync features out of the box. This is a challenge to many people because it works so well on phones that you kind of want to make sure you are syncing your phone and whichever computer. I have a work computer (Windows), and personal computer (Linux), and an Android phone.
I initially was syncing with Google Drive, this worked well but the Linux aspect was a little clunky. I had to remember to manually pull push using the command line, which is fine but something in Obsidian would be better.
Then I tried Obsidian Git. I love Git and use it at work and in my personal life. It was great except that I would occasionally hit merge conflicts. These didn't result in data loss since everything is locally committed but it could be hassle to resolve, especially on my phone, especially when I just want to pull up a grocery list.
Finally, I realized for about $0.30 a day, I could support the company that makes this amazing software and have a trouble free experience. I signed up for Obsidian Sync that day, signed into the account on all my devices and haven't looked back. My vault is still synced to Google Drive (or for my work vault, OneDrive).
My primary uses:
Journal - I use Daily Notes in Obsidian to keep a note on each day. I log things like what I did that day, if I had some symptoms or other to track (e.g. first day of a cold, food that didn't agree with me), if I do some maintenance around the house, and so on. Just normal stuff.
CBT - sometimes I need to vent or sort out my thoughts on something. I don't like to burden others and often times my thoughts seem trivial or immature when I write them out. This is a good way to both vent my feelings and also put them in perspective. If I do this a few times and something is still bothering me, I'll take care of it but sometimes I realize a nagging through or idea was just nonsense.
Task manager - I put all my tasks into Obsidian. Using the Tasks plugin (or Dataview) you can easily produce reports which tell you which TODO items to focus on at a given time, they are easy to review, sort, and filter, and I can scatter them everywhere throughout daily notes, project docs, and informational notes.
Project Docs and Notes - If I am working on something, I'll start a project document. This is just a place I keep notes on what I'm doing like a contractor's phone number, or the three headphones I am wavering on, or maybe a sketch and some dimensions for a shelf I want in the garage. I also keep regular notes (what's the WIFI network, how do I shut down the air conditioning in the Fall, lists of shows I am currently watching or want to watch, etc). This is just pretty poorly organized text notes with the odd picture or diagram. The nice thing is with searching, tagging, and other metadata it is trivial to find what I need without obsessing over organization.