Zotero is a free, open source reference manager tool for both MAC and PC. You can use Zotero to keep track of your references (books, articles, websites) and drag them into your document as in-text citations. With this program you can get help with making in-text citations and generate a bibliography in a quick way. You can also collaborate with others at collecting references, e.g. for an essay you are collaborating on.
Free access to Zotero
Zoteros own support