Beeminder : +6 : Using it for nearly 2 years with good success in most areas I select to 'Beemind'. Yet to have to pay out on any goals (though I have derailed on no-pledge goals on 2 occasions).

RememberTheMilk : +2 : using it for several years. Best use is to keep track of tasks I have and have not done, but not great on committing me to action. Best suited to keeping track of minor tasks, especially recurring ones.

Trello : +2 : Used for perhaps a year. Similar experience to RememberTheMilk, but better suited to more complex tasks and projects.