Zotero is a free citation manager, similar to EndNote. While the library officially supports EndNote, you are welcome to try out this software option as well.
Zotero allows you to create your own personal database by importing references from online databases and sources. You can use these references when writing papers to automatically format in-line citations and bibliographies with the correct citation style (APA*, AMA, etc.)
After you download the desktop software, you can sync your local collection to the cloud so you can use Zotero on multiple computers. Your collection is synced through the Zotero servers (unlimited storage) and items synced to the Zotero servers can be accessed online through your zotero.org account.
The Zotero Standalone is a separate, browser-independent application, but you'll also need to download the Firefox or Chrome browser extension. This option makes it easy to scrape citations from web pages and add them to your citation library.