I receive a lot of emails and, although I know I am not supposed to, I use my Outlook email inbox as a todo list 
If an email requires an action from me that I cannot respond right away, I flag it. If I send an email and have assigned a task to someone else I need a reply from, I assign a category (colour). All the people who report to me have different colours (they don't know that!), so I can quickly see how much each person owes me by going down my email inbox to spot their colours. Once that person gets back to me, I file the email away and flag it, if it requires an action from me or categorise it if I assign the task to someone else.
If I don't expect a reply from someone until more than a week away, instead of categorising it, I file that email away, so it does not clutter my inbox. I put an all day reminder in outlook to myself to check in 2 weeks' time whether that person has replied, attaching the email to my calendar invite. If they did not, I go off the back of the attached email to chase.
Other than the above, there are bigger projects like writing reports, or hiring new staff or giving training. For these, I just have pieces of paper (about half of A5), which I keep next to my computer and cancel out the tasks once I finish or create a new list if it gets too untidy. I currently have 4 such lists. They usually shake out to when the tasks are due. I have a long term list (probably will never get round to them until I retire), medium term (next month or so), short term (within the week) and immediate (for tomorrow).
I put outlook reminders in my calendar to myself. For example, if I have to present at a meeting on 15 Jan, I put a 2 week reminder to that meeting reminding myself to do the slides. I keep snoozing that reminder until I have done the slides.
When I attend a meeting, I take meeting notes which will have actions. Once the meeting is over, I may send emails (categorise) or put reminders to myself or put it on a list.
Cannot believe I wrote all that. I juggle a lot of tasks in my professional and personal life and manage the home diary. My Outlook calendar is the comprehensive calendar of both my work and personal life. It is pretty busy looking!
The above is somewhat primitive, but seems to work for me. I get things done and things don't unintentionally slip the net. If I drop balls, it is because it had to be de-prioritised.