HEY - Email at its best, new from Basecamp.
Todoist - Todoist is a to-do list that helps you get organized, at work and in life.
Horde - Horde Groupware is a free, enterprise ready, browser based collaboration suite.
TickTick - TickTickis a cross-platform to-do list app & task manager helps you to get all things done and make life well organized.
InstAddr - Disposable email address application.
Remember The Milk - Remember The Milk is a task and time management application for mobile devices.