Zotero is a free, open-sourced research tool that acts as a citation generator and organizer. Citation formats supported by Zotero include APA, MLA, and Chicago. Zotero has additional features like the ability to extract source information from online resources into Zotero, so you don't have to manually enter citation information. You can sign-up for a free Zotero account by visiting the registation page.
Note: To access some features of Zotero, you need to download it. You can choose to download it as a browser extension or as a stand-alone application.