GTasks add-on for Google Docs integrates your Google Tasks with Docs, allowing you to tackle your to-do list and manage them effortlessly.

Free Features:
 * Create tasks by selecting your document text
 * Manage by add, delete, mark as done, specify due date
 * Nest subtasks within a task  

Premium Features:
 * Create new, rename, delete tasklist
 * Edit inline, rearrange tasks by drag drop
 * Paste the task to the document in a click