My todo app of choice is asana (http://asana.com http://asana.com). You can start from a simple todo list... but each task can have sub-tasks, dates, attachmen

My todo app of choice is asana (http://asana.com http://asana.com). You can start from a simple todo list... but each task can have sub-tasks, dates, attachments, etc. Meaning that you can add hierarchy and additional information if you need it. It also has mobile apps, at least for iOS and Android.