Invision - Prototyping and collaboration for design teams
EssentialPIM - EssentialPIM is a free Personal Information Manager that keeps up with the times and lets you manage appointments, tasks, notes, contacts, password entries and email messages across multiple devices and cloud applications.
Marvel - Turn sketches, mockups and designs into web, iPhone, iOS, Android and Apple Watch app prototypes.
Todo.txt - Track your tasks and projects in a plain text file, todo.txt. A todo.
UXpin - Design is really about solving problems. UXPin is the UX Design Platform that gets that right.
Task Coach - Task Coach is a simple open source todo manager to keep track of personal tasks and todo lists.