Zotero http://www.zotero.org/ is a free extension used with the Firefox, Chrome, Safari and Edge browsers. It will help you collect, format, and cite your references in a number of citation styles including APA, AMA MLA, and Chicago.
Mendeley is a free reference management system supported by Elsevier. Using this tool you can generate citations and bibliographies in a whole range of journal styles and include them in your writing.