Todo.ly - Todo.ly is an intuitive and easy to use online Todo list, and Task Manager. It helps you to get organized, simplify your life, and to get things done. Create todo lists, and manage them online from anywhere.
Sortd - Rated the #1 App for Gmail
TaskUnifier - TaskUnifier - Task Management Application
KanbanMail - A Kanban board for your emails.
Doit.im - Doit.
Trello - Infinitely flexible. Incredibly easy to use. Great mobile apps. It's free. Trello keeps track of everything, from the big picture to the minute details.