Sure, I dump most everything that comes to mind, to dos, reminders and even long multiyear projects into Omnifocus (OF). You can dump everything into the inbox at first as it comes to mind and then when you have some free time, hash it out into its own project or action. The default shortcut (I think) to invoke the quick input window is ctrl+option+space. I use this probably about 20-30 times a day as quick thoughts pop up to save for later.
Stuff that has an item associated with it can hang out in OF as well. For instance if I need to reply to an email or complete a PDF, I can drag the file ref into the item in OF and the link will show up there, so I don't even need to remember where I put it. More importantly, if I need to walk away from it,
The most important part are probably the date/time related items. Most anything can sit in OF, important things that are due at a certain time. Use OF to capture the data and give it the due date of the item. OF can, optionally, publish a calendar subscription that you use to connect to your calendar of choice (I use BusyCal). Now these items will be managed in OF but you can see their due dates on the calendar.
OF for iOS is just as powerful as the desktop companion though not free, also worth the price. They have a free sync server but you can use your own webdav server (which I recommend, just to maintain control of your data).
If you are really hardcore you can use location based context. For instance you can have it remind you of your grocery list when you're at your local grocery store. Encryption/Password options are also available.
here are two links to get started, the first is from the Omnigroup, the second (paid) option is from the guy who invented the GTD methodology and how to apply it to OF.
https://inside.omnifocus.com/gtd
http://gettingthingsdone.com/2014/09/new-omnifocus-2-setup-guide/