What is the oldest collection of code out there, including different versions of the same project, where someone could access it and compare the changes between versions to get a sense of what changed?

By publicly-available, I mean where it is made available for anyone who requested it to somehow access it (e.g. from the internet, from a library).

With "repo," I'm not imagining it using version-control software per se, just that it could be compared and clearly show some kind of iteration of the same piece of code.