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 :)
>"The growing number of complex components made it difficult to retain an open source version stripped of our internal specifications. This complexity is the main reason that we archived the open source Scribe project. The current version of Scribe’s architecture is detailed below, with a focus on the components that comprise the data plane. ". Quoted from the article.
Interesting! Just found out about this, and I googled it out. TIBCO acquired Scribe Software, and Scribe Software was running as early as 1998-1999! :D
The initial stuff seems to not be so related, but the current description of what they do seems much much closer to what Facebook's Scribe does today :)