The Craft of Research by 
Zotero is a free, easy-to-use tool to help you collect, organize, cite, annotate, and share research. It helps you track all your sources and build bibliographies in minutes! It's also collaborative, so if you're working on a project with multiple people you can all save your sources in one place!
Zotero 7 was just released with a new logo.
Check out Zotero's extensive documentation to see how it works!