And that is just on GitHub. That doesn't count what was done on SourceForge and Assembla,

That is a momentous occasion! Thank you for putting this into the spotlight.

With the new 2.0 coming around the corner and also some movement in our newly-minted ImpressTNG branch, that number of PRs is certainly going to rise even more!

Over the years, we have used different version control repositories, our current one being GitHub. A recent merge of a pull request has pushed us to 1,000 pull requests that have been merged into our core - https://github.com/ImpressCMS/impresscms/pulls

Thanks for all the efforts that have gone into bringing us this far!