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

Purp - A smart to-do list and goal tracker app

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

Nirow - Habit tracking: Automated, Siri-ed, Calendar-ed, and More!

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.

Things - Things is an easy to use task manager.