My new bestie in the systems/tools world is EVERNOTE (affiliate link). Have you used it? I tried to use it in the past, but for some reason I didn't embrace it. (OK, past meaning like 5 years ago or so...) . I think there's probably been some functional upgrades.
The main reason I decided I LOVE it is the free document scanner app (Scannable) that I can use with my iPhone. All you do is download the app, connect it to your Evernote account, and it puts any of your hand-written notes, printed documents, receipts, etc. all into Evernote for you. This is SUCH a time-saver. I took my old notebook that I carry with me everywhere and scanned my pages that had information I wanted to reference easily into my Evernote, and now I can reference that paper notebook from anywhere!
Evernote in itself has a free version, and I think it will help most people with their day-to-day needs. There are upgrade options available for additional search and sharing capabilities.
Next, meet Todoist. I've been playing around with it for a few weeks now, and it's pretty slick. You can create as many project categories as you want (well, up to 80 on the free version, but do you REALLY need more than 80?!), and sort all of your to-do's accordingly. Each one can be assigned a recurring or one-time date (or no date at all), using real language. What does that mean? If you type "eat breakfast daily", Todoist recognizes that it should add "eat breakfast" as a recurring daily task.
I highly encourage you to use these two tools together - Evernote and Todoist. You can easily add a reminder to a note in Evernote that you need to follow up with, and have that task show up in your Todoist, to keep your list in sync. The apps easily connect with Zapier (one of my most favorite tools ever).
Have you ever been in a conundrum where you have a bunch of different to-do lists? Yeah, me too. Being able to keep all my lists in one place is a lifesaver.