Zotero is a FREE citation tool that you add to your web browser, or use as a standalone application.
You have two options for using Zotero:
1) Download Firefox Extension (for Macs and PCs)
Choose this option if you exclusively use Firefox or if you have a PC.
2) Download Standalone Version for Mac (Mac only)
Choose this option if you have a Mac AND you want the flexibility of using your choice of Internet browser (Firefox, Chrome, or Safari).