Google Task -Gmail

Use Google Tasks to keep track of the things you need to do. You can create lists of items, set due dates and notes, and even add Gmail messages directly to Tasks.
 Using Google Tasks in Gmail to get started, click the down arrow next to Gmail in the top left corner of your Gmail page, then choose Tasks.
To enter tasks, click in the Tasks window and start typing. Once you've typed in a task, press 'Enter' to create another task or use the + button at the bottom of your list.
Here are some of the options available in Google Tasks:
Google Tasks Keyboard ShortcutsUseful keyboard shortcuts for Gmail and Google Tasks are listed here:
Tackling Gmail Tasks
GMail Tasks - Tasks on Google Calendar