Over the years I have tested many To Do apps, both stand-alone and web-based and of various levels of sophistication. They all had some claim to fame, but I abandoned most of them as not sufficiently helpful for proactive planning. Eventually I developed a small set of knockout criteria for selecting an effective planning app:
The app must have what Outlook so sorely misses: it needs to have the ability to work with subtasks or subprojects, or it should sport some other way of subdividing larger projects into logical groups of concrete actions.
It must be able to quickly and efficiently absorb important emails, either as task, note or file, with link-back ability to the original mail so I can a) quickly find it and b) answer it if needed.
The app must be capable of storing meeting minutes, notes or core files of the project within the app. So the most relevant information is kept together in one place and is quickly accessible.
The app must provide visual overviews which show a project timeline and enable quick changes and additions in that timeline. Think of a simplified Gantt chart.
Of course there are several other criteria that are highly desirable too, but these four must absolutely be met. The first criterium was easily met, a lot of ToDo apps can do that. The second criterium, about emails, turned out to be more problematic, it excludes most web-based solutions for instance.
The third thing, about keeping crucial information at hand, can be done in several apps, all be it usually in a rudimentary fashion, with documents tucked away in the Note field of some task. Which means that they disappear into an archive when that task is marked as completed. Not exactly an effective way of storing essential info.
A good example of a very powerful app that can do the first three things but not the fourth is Organize Pro. Want support for Kanban, WBS, basic mind mapping, online team cooperation? Need an extensive tagging system, syncing between devices, data security, report tools? The app has you covered. See taskfabric.com.
The fourth criterium, about visualisation of project timelines, turned out to be a real knockout condition. I know of just one app that meets all four criteria. It is called Pagico. It is an amazingly effective tool with a beautifully designed interface. Facilitates team cooperation, medium and long-term planning, has Gantt-like timeline charts. Uses project workspaces that contain all relevant files, notes, links and planning aids. Can sync all that between all your devices. Has extensive tagging and filtering systems, data protection and much more. Check it out at pagico.com.