Taskums

Free Email Based Project Management Software. sends emails to your team informing them of their tasks and they click a button in the email when the task is finished. It couldn't get any easier to collaborate online than this.

How does it work?

1. Create projects and assign people responsible for each task by their email address.
2. When the task is active, an email will be sent to the person responsible for that task.
3. After completing the task, they click a button in the email.
4. Rinse and repeat until entire project is finished.

Although they say it's free, it's quite limited as a result, but there are various pricing plans available.