That's what I originally envisioned with DuctMail. It's a simple reminder system at the moment, but the basic idea was:
command@ductmail.com
Subject: Plain English Arguments
Body: whatever else we might need.
For example:
Email: reminder@ductmail.com
Subject: Today at 5PM
Body: Buy milk!
Also, don't forget to buy some KY, and a lawn chair.
The problem with other systems is they usually try to put the arguments into the email.
I'm working on a todo system as well.
Email: todo@ductmail.com
Subject: Name of Todo List
Body: One Todo
For Every line
Of the email
Sends you a reminder every so often, and you can reply back with what you've accomplished by putting a - in front of the item.
Their are other ideas being worked on. One I'm trying to find time to finish up is a daily habit system.
It would email you in the morning reminding you what you want to do every day, and then at the end of the day, it will email you, asking you for an update on how you did, and you could reply back, etc.