Zotero allows you to collect, save, and manage bibliographic information on books, articles, websites, and more. Once you've got Zotero working, you can use it to create in-text citations and bibliographies in over 7,000 styles with the click of a button. Zotero integrates with Word, Google Docs, or LibreOffice, or can just export a bibliography to pages or any other word processing program.
Zotero is available for Mac, Windows, or Linux. If you're on a Chomebook, iPad, or other mobile device, you can use zBib instead. It's browser-based and should work anywhere.
In addition to Zotero itself, you will need the Zotero connector for whichever browser you use. Connectors are available for Chrome, Safari, Firefox, and Opera.
If you have a Chromebook, are using a phone, or don't want to install a program, you can still get many of the benefits of Zotero by using ZBib. Zbib allows you to make a bibliography in any style by adding the URL of your item. It won't help with in-text citations, but it still saves a lot of time!