The following are the requirements for the To Do List module.
The basic To Do List module offers you a new Node type and several User lists. There are no specific requirements for the main module to work other than Drupal Core.
The Block module is mandatory, so in itself it is not a requirement.
In order to use the To Do List Block sub-module, you need the Core Block module.
This option gives you access to a block that you can add to one of your regions. By default, it displays the items that are close or past their deadline.
Check out the To Do List Block feature for more information.
The Views module is optional. It is necessary if you want to make use of the To Do List Views sub-module.
This option gives you a way to create your own lists of To Do List items. It respects the permissions even if the View access settings are not set by the Views maintainer.
Examples of lists one can do:
Check out the To Do List Views feature for more information.
The Trigger module is optional. It is necessary if you want to make use of the To Do List Action sub-module.
This option gives you the possibility to control events that the module sends when something happens. There are many things that can be handled such as reminders and status changes.
Check out the To Do List Actions feature for more information.
The Rules module is not yet supported. It will be optional once available. This will be added in order to give better event hanlding than the Actions sub-module. Stay tuned.