A while ago my friend and colleague Greg Newman recommended https://teuxdeux.com as a task manager. I've tried a lot of different task managers but none have really stuck. TeuxDeux has.
I think the main reason is it takes such a simple approach. There's no attempt to have projects, tags, contexts, priorities or anything like that.
You just have a list for each day plus labelled lists not attached to any day.
Items not completed on the day just get moved to the next day. Markdown is supported in items and I sometimes use this to make little headings to separate tasks into sub-lists (--- also works nicely as a separator). There is very basic support for recurring tasks.
What I like most about the approach is:
Regarding the third point, I'll note that I don't use it for all my lists of things (I use https://workflowy.com for that) but it's nicely to have a few lists easily viewable. Although they claim it's useful for Someday / Maybe items, I prefer those not to clutter my thoughts on a daily basis so I put them in workflowy and use the non-date lists in TeuxDeux for things like monthly or quarterly goals, daily routines, etc.
If you're well setup with something like Todoist, Things, or Nozbe, you might find TeuxDeux a little too basic but if you've found you can't stick with one of those heavier tools, and are really looking for something just slightly better than a text file or physical note book, TeuxDeux is worth checking out.
One final thing I find interesting about TeuxDeux: the developers say it's complete. It does what they set out to build and they aren't adding new features just for the sake of it. That's refreshing approach and I think it's worked well for this product.