Citation management software (i.e., citation managers) can help save you time by formatting footnotes and bibliographies for you in the citation style of your choice. In addition to being a great tool for academic writing, citation managers can also help you collect, organize, and annotate information sources (including full-text PDFs) for other purposes.
Zotero is the only citation management system that currently supports the McGill Guide style. For more information, see Legal Citation Management with Zotero.