Ativiti looks cool, but in this article they say that the user shouldn't have to do anything differently, yet they call themselves a `platform'. I haven't actually tried the app, so maybe it isn't fair to say, but if I see `platform' I usually think of complex all-encompassing products that require some integration.
I think one of the reasons that there are so many apps that could be considered task management apps is that everyone has different ideas on what task management is. Also, there is some value in having local task items that are available in the tools that you already have at your disposal, ie Outlook. For us (shameless plug: http://www.ubernote.com), we wanted to have task lists inline in notes where we already had data, so we added the feature. Add one more app to the list....
I think one of the reasons that there are so many apps that could be considered task management apps is that everyone has different ideas on what task management is. Also, there is some value in having local task items that are available in the tools that you already have at your disposal, ie Outlook. For us (shameless plug: http://www.ubernote.com), we wanted to have task lists inline in notes where we already had data, so we added the feature. Add one more app to the list....
Good luck with Ativiti