Fitter, happier, more productive

Unless you're an organisational genius, you need help with your life. I'm not, so I do. These apps have helped me to get more organised and haven't cost me a penny...

Evernote
How Wikipedia describes a commonplace book is basically what Evernote is for me:
...a way to compile knowledge, usually by writing information into books. Such books were essentially scrapbooks filled with items of every kind: medical recipes, quotes, letters, poems, tables of weights and measures, proverbs, prayers, legal formulas. Commonplaces were used by readers, writers, students, and scholars as an aid for remembering useful concepts or facts they had learned. Each commonplace book was unique to its creator's particular interests
I use it especially for storing great quotes and snippets of information, articles from websites and other media that I know I'll want to read or refer to again, notes from talks I've listened to and books I've read, as well as recipes and photography tips. You can tag the notes with whatever descriptions you like, it's fully searchable, and like all these apps it works across different devices so I always have everything with me. It's like a spare brain.

Simplenote
I make notes of thoughts, short-term tasks, and little things like that all the time which means I like to have access to those notes wherever I am and whatever I'm doing. Simplenote makes this happen on my phone, my tablet, and my computers at home and at work. Because I only use it for small stuff, it doesn't take a huge effort to get up and running as Evernote does. It also looks nice.  The only minor annoyance is that syncing from my phone when WiFi isn't on can cause bits of notes to disappear. I've decided it's worth that hassle to save the much bigger one of not having access to all my notes all the time.

Workflowy
A good organising app will work in the same way that you think, and Workflowy does that for me. I have lists of things to do, and then lists within those lists of things that I need to do for each different area. I think that way, and this app lets me write it all down, which helps me feel confident that even if I'm not dealing with an issue right now, I won't forget it - so I don't need to think about it now and can concentrate on what I'm doing.

Pocket
This used to be called "Read it later" which is less catchy but does explain what this app is about. Seen something online that looks interesting but you just can't give it your attention right now? Save it to Pocket and you'll be able to come back to it when you're ready, on a different device if necessary, and it will almost certainly be displayed in a better layout than where you first saw it. It's slightly trickier to set up than some of the other apps but is worth the investment.