Gists are actually Git repositories, which means that you can fork or clone any gist, even if you aren't the original author. You can also view a gist's full commit history, including diffs.
Each gist indicates which forks have activity, making it easy to find interesting changes from coworkers or complete strangers.
If you want to make local changes to a gist and push them up to the web, you can clone a gist and make commits the same as you would with any Git repository. For more information, see "Cloning a repository."
Viewing gist commit history
To view a gist's full commit history, click the "Revisions" tab in the right sidebar.
You will see a full commit history for the gist with diffs.