[Scooty]

They're both libraries for building user interfaces. They're related because they both solve the same problems. They also share a lot of core ideas (one way data flow, reusable components, declarative UIs, etc). I'm pretty sure React came first and heavily influenced Vue. They aren't commonly used together because most projects only need a single UI library.

[nirvdrum]

Thanks, but the parent seemed to imply one was a commercial offering and copied by the other as an open source project. That's the part I was looking to get clarification on.

[acemarke]

No, they've both always been 100% open source (ignoring the complaints about React's previous BSD+PATENTS license). React is built by Facebook, while Vue is primarily built by Evan You (+ a team of core contributors).

The "copying" comments are largely due to things like Vue's new proposed hooks API being very much inspired by React coming up with hooks in the first place.