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Mark Claypool has written an implementation of BBR for ns-3, a popular network simulator.
A simplified BBR implementation has been written as part of the Congestion Control Plane (CCP) work at Stanford.
History/Related Work
There is another instance of "BBR TCP", namely Bufferbloat Resistant TCP proposed by Michael Fitz Nowlan in his 2014 Ph.D. thesis (Yale library catalog entry, PDF). It shares the basic goals of (Google's) BBR TCP, namely to detect bottleneck rate and to avoid bufferbloat. But it uses a delay-based measurement approach rather than direct measurement of the amount of ACKed data per time, and doesn't seem to make use of pacing. Despite these differences, the link between the two BBR TCPs seems more than just a coincidental acronym collision: Fitz Nowlan is acknowledged in the Queue/CACM papers, and conversely acknowledges several of the "Google" BBR authors in his thesis.
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