The only thing that Github's pull request system adds that wasn't being done before is single-click merging. Everything else was there. You would email a patch

The only thing that Github's pull request system adds that wasn't being done before is single-click merging. Everything else was there. You would email a patch to the author, or to the mailing list, and discuss the merits of the patch there. Then someone with access to the repository would commit it (I use the term generically; version control was less common back then). The diff program we all use today has it's origins in the 70s, although the unified diff format that we almost always use was created in the 80s. Email was invented in the 60s, UUCP in the 70s, and Usenet in 1980. Version control was invented in the 70s with SCCS. Web-based bug trackers such as Bugzilla originated in the 90s, as did continuous integration software like Tinderbox. Of all of these, Git represents the biggest improvement over it's predecessors, while email is pretty much still just email. The diff program hasn't changed since the 80s. Bug trackers and other such tools haven't changed dramatically either, although a lot more attention is paid to UX and polish these days. I think the largest change is the wide availability of these tools today. Everyone knows about them, and it's seen as aberrant to not use version control or bug tracking.