Strike for macOS is a powerful outlining app that offers collaborative editing, attachment management, and smart text features such as Markdown support and the use of tags.
Skribal is a free mobile app for readers everywhere. Skribal lets you find the books you're reading and make notes in a central, easily accessible place. Looking for that key quote from the last book you read? Can't find that inspirational epilogue that motivates the hell out of you? Not anymore. Access all of your reading highlights in one place