Streaks - The to-do list that helps you form good habits.
Todoist - Todoist is a to-do list that helps you get organized, at work and in life.
Taskful - Deadlines, meet your match.
Mendeley - Easily organize your papers, read & annotate your PDFs, collaborate in private or open groups, and securely access your research from everywhere.
Zotero - Zotero is a free, easy-to-use tool to help you collect, organize, cite, and share research.
ToDoList - Windows desktop application to stay on top of your daily tasks.