There is *no lack* of to-do apps designed at least somewhat around [Getting Things Done][1] - just see the answers to [this question][2], for example. I'm a user of Things on iOS and have heard a lot about OmniFocus, but I've never gotten a good recommendation for an app that can manage to-dos *for more than one person*. 

My wife and I are looking to adopt a GTD-inspired workflow for a variety of personal projects, some shared, some individual, and it would be ideal to manage these projects side-by-side.

Short of us each running our own instance of a given app on our separate devices, and including iOS / OS X synching among my requirements, do any of the flagship GTD to-do apps offer the concept of projects and to-dos that belong to a specific person of several?

  [1]: http://en.wikipedia.org/wiki/Getting_Things_Done
  [2]: http://apple.stackexchange.com/questions/10717/what-is-a-good-gtd-app-with-cloud-sync-on-iphone-ipad-and-mac