RxJS

Before RxJS had a single canonical home at ReactiveX/RxJS, there were two parallel implementations: Reactive-Extensions/RxJS (Microsoft, 2014) and ReactiveX/RxJS (the open-source fork, 2015). Microsoft archived the Reactive-Extensions repo in 2018 after donating the spec to ECMA TC39. The "archived" version is the one people still search for and the one with the most Stack Overflow answers. The maintained version is at github.com/ReactiveX/RxJS, but the archives are 500MB of PRs and issues. The original maintainers (Matthew Podwysocki, Erik Meijer) both moved on; Matthew to Microsoft Research, Erik to Facebook/Meta. Anyone who wants the original commit history has to clone the archived repo.