Google Tasks is a standalone application, similar to the Gmail tasks that allows todo lists. Tasks can be nested within one another, and add notes to any task. If you create a task in one application, it will show up in the other. Once a task is done, you can add a check mark and it will appear with a strike-through.  You can also set due dates, users can create, edit, and delete multiple task lists. But only the default list will be shared with your Gmail account.

More info: Google Tasks

Update: Mistakenly poste, Google has removed the page, and the URL no longer works.

Source:→ Google Blogoscoped