Gone - An ephemeral to-do list

Todoist - Todoist is a to-do list that helps you get organized, at work and in life.

Simpli - Keep track of email, calendars, notes and more in a unified interface.

Mendeley - Easily organize your papers, read & annotate your PDFs, collaborate in private or open groups, and securely access your research from everywhere.

RescueTime - Time management software that shows you how you spend your time & provides tools to help you be more productive.

Zotero - Zotero is a free, easy-to-use tool to help you collect, organize, cite, and share research.