GQueues

The idea for this app is great and the 2-way sync with Google Calendar is the biggest part of it. However, that being said, the app itself has been lagging behind on development so much that I can't recommend it anymore for those looking to manage projects. It's great as a simple list maker but the developer has decided to focus more on collaboration features when he should be focused on features that make using the software itself great. As it is, I believe apps like Todoist are passing this app up in development and 2-way sync with Google Calendar. For as long as the software has been around, there are certain features that are basic and necessarily to an app that handles projects that should have been developed by now.

Examples of this are the inability to select multiple tasks at once to move from one queue to another. For example, if I want to move several tasks from the Inbox to another queue, I can't do so at the same time. I have to move each one individually. This is a long requested feature for years now and although it has just now been added to the roadmap, who knows when it'll be implemented.

Inconsistent behavior between web app and mobile apps. If you delete a parent task that has subtasks in the web app, you'll get a pop up notice letting you know you're about to delete a top-level task with subtasks. However, in the mobile apps you don't which is bad since parent tasks are not indicated at all. This means you may accidentally check off a parent task thinking it was a single task.

Supports tags, hierarchical lists, dates, and sharing lists(queues) with others. The best applivcation for GTD I have found yet. Very good integration with gmail and google calendar. Mobile version(requires html 5 browser) works fine both online as well as offline.