Getting Things Gnome! is an organizer for the GNOME desktop environment
GTG focuses on usability and ease of use. Its main objective is to provide a simple, powerful and flexible organization tool to the GNOME desktop environment.
GTG uses a very handy text edition system for task creation and edition. The task editor can automatically recognize metadata such as tags and subtasks only by the use of a very simple syntax. If you wanna know more about this, please read Getting Started With GTG.