Very interesting, the name basically gives the game away.
You give the tool a list of git(hub) repositories and a command (or more advanced script files) and it runs it against them.

You could for example create a file in each one. Or change some variable. Or grep and sed something from one thing to another thing. Or or or.

Honestly not seeing myself using it that often - but the fact it exists is fascinating to me, and the naming is just genius. Though I am a little sad that it seems to only work for Github projects.