Purp - A smart to-do list and goal tracker app
Todoist - Todoist is a to-do list that helps you get organized, at work and in life.
Gone - An ephemeral to-do list
Mendeley - Easily organize your papers, read & annotate your PDFs, collaborate in private or open groups, and securely access your research from everywhere.
Things - Things is an easy to use task manager.
BibDesk - BibDesk is an organizational software created to help you edit and manage your bibliography. It keeps track of your bibliographic information as well as said information's associated web links and files. Read more about BibDesk.