Both Appigo ToDo (app/web) and Toodledo Pro (app/web) have the idea of a "project" that can contain subtasks.
For small projects I don't bother with the overhead of project creation and task maintenance. Instead I create a single task that I edit when I complete a 'step' in the project. It lasts the life of the project.
Each time I complete a step, I edit the task to add a new "next step" and I date stamp the completed step. I also keep short notes in the body of the task note.
For example, if the task is "Update Passport" I might have the following my "notes" section:
- schedule photograph
- download form
- complete form
- schedule appointment .. etc.
In practice I don't usually write out all the next steps. I just write out the one that's up next. For A tasks I may schedule a calendar appointment too.
Similarly I don't bother with repeating or recurrent tasks. I create one task, and just reschedule it as needed. My "pay visa bill" task has been moved forward one month at a time for years. (Periodically I delete the list of dates I paid to shrink the notes section).
- GTD: Create appointments not tasks
- GTD: Introduction to a series
- Appigo Todo.app and Todo Online: best solution for most
- Toodledo: power user solution, best import/export/integration. Lacks full text search (!).