Todoist - Todoist is a to-do list that helps you get organized, at work and in life.
Purp - A smart to-do list and goal tracker app
Mendeley - Easily organize your papers, read & annotate your PDFs, collaborate in private or open groups, and securely access your research from everywhere.
Gone - An ephemeral to-do list
Zotero - Zotero is a free, easy-to-use tool to help you collect, organize, cite, and share research.
Things - Things is an easy to use task manager.