brain is a web-based todo app for implementing David Allen's Getting Things Done® methodology. It supports assigning tasks with contexts, projects and tags, as well as start and due date, in order to provide you with the tools to keep on top of your tasks at all time.
The core David Allen's GTD method is to keep all your ideas and tasks in one safe system so you don't have to think about them until you either go through them to plan further or actually do something about them. After having ordered and planned everything, GTD is supposed to let you know at any time, what your next action can be. (Note: This is a very, very short and probably equally wrong description of the GTD principles. If you want to know more about it, Wikipedia might be a better place to start.)
Read the docs for details on how to set up and use brain. You can also have a look at the demo.
NOTE: Even though brain is a PWA, which is supposed to sync between multiple devices at some point, it currently only uses local storage in the browser (specifically the IndexDB). The synchronization server is currently not implemented. If you need multiple-device synchronization, either wait until it's done or contribute..
Note: (another one) brain is in no way endorsed by or related to David Allen or his company.