This is DoX (as in do <X>, where X is a task, but also pronounceable like “docks”).
All your tasks are stored in the browser, and you can even load up this page whilst offline in order to manage your tasks.
You can read more about DoX on the about page.
~includes a longer description of the task.
!symbol sets a task's priority, a number between 0 (low) and 3 (high).
@denotes a due date and time for the task. This can be a date, or a date and time. Write it as
&defines a repetition rule. This can be a number of days before the task is due again, counting by default from task completion, or from the previous due date by adding
*after the number of days.
#adds a tag. A task can have any number of tags.