React, Flux, GraphQL, Hack, HHVM...? All of this and more!
Yarn is a new package manager that replaces the existing workflow for the npm client or other package managers while remaining compatible with the npm registry. It has the same feature set as existing workflows while operating faster, more securely, and more reliably.
This is a pragmatic solution to the problem that cost the corporation quite a bit of money and resources. While development of Yarn was not free, it will surely pay itself back in increased efficiently. Naturally Yarn is Open Source, so all of us can benefit from the work done by Facebook engineers. This is similar to other Open Source efforts from Facebook such as React, GraphQL and HHVM.