Task List - Personal task manager and to-do list app for iPhone and iPad
Todoist - Todoist is a to-do list that helps you get organized, at work and in life.
Habitify - The easiest way to keep track of your habits
Mendeley - Easily organize your papers, read & annotate your PDFs, collaborate in private or open groups, and securely access your research from everywhere.
Capsicum by Illuminated Bits - Plan your day. Track your habits. Tell your story.
Zotero - Zotero is a free, easy-to-use tool to help you collect, organize, cite, and share research.