Trello is a simple project management tool, but it can also shine as your personal GTD task management tool. The web app's boards, cards, checklists, labels and other features make it easy to view and manage your tasks, much as you would use index cards on a cork board.
Programmer and writer Josh Earl has detailed his Trello-based GTD system. He has boards for next actions, projects, goals, someday/maybe and project-specific boards. Within each of those boards he has lists. For example, under projects: active, waiting for, needs clarification.
Some features of Trello he points out are perfectly suited to the small-tasks management of GTD include how easy it is to: group related tasks and move them into full projects, copy boards (use them as templates) and add supporting information to each task or project.
After trying just about every task management system out there, he says Trello is "about as close to a perfect platform for GTD" as he could imagine. Read his blog post for more reasons why and to take a peek at his GTD setup.