Todoist - Todoist is a to-do list that helps you get organized, at work and in life.
Mendeley - Easily organize your papers, read & annotate your PDFs, collaborate in private or open groups, and securely access your research from everywhere.
TickTick - TickTickis a cross-platform to-do list app & task manager helps you to get all things done and make life well organized.
Zotero - Zotero is a free, easy-to-use tool to help you collect, organize, cite, and share research.
Remember The Milk - Remember The Milk is a task and time management application for mobile devices.
Qiqqa - Qiqqa is a free research and reference management software. It can be used in many organizational projects from the academic to the personal to the business endeavor. Read more about Qiqqa.