The version that was open-sourced kept evolving and integrating with other internal systems at Facebook. That's what made it hard to continue open-sourcing it (why the open-sourced version was discontinued) and why the current version is also hard to open-source.

Maybe one day we'll have a version available. In any case, one of the larger parts of the system (LogDevice) is open source :)

(disclaimer: I work in Scribe)

LogDevice: https://engineering.fb.com/core-data/open-sourcing-logdevice...