For comprehensive content and task management, the best software I ever used was ACT!

It's been years and they've been through a couple of changes of ownership (in fact, the reason I stopped using it was they stopped supporting the Mac ) - so I can't really speak to how it is now for sure, but I loved that software.

It's designed for salespeople, but it was enormously customizable to the extent that it was just perfect for a solo law practice.

And they do have a mobile app that works together with the desktop.

For just basic to-dos, at this point I put them into my regular calendar, and either make something an all-day event with an alarm during the daytime, or assign a particular time to it even if it doesn't need one.