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git - the simple guide One of the simplest and most straightforward guides
Git CheatSheet - I really like the layout on this page
Things I Needed to Learn and Thought I Should Bookmark It for the Future
What happens when the repository owner has not prepared a zip file, and you just want a download to use yourself? There is an answer and you don't need to go though that horrid process to download software, install and register keys and whatnot on GitHub, etc.!
To simply download a repository as a zip file: add the extra path '/zipball/master/' to the end of the repository URL and voila, it gives you a zip file of the whole lot.
It then gives you a zip file to download.