And, if one wants to be picky, Pauseless is a variation of Henry Baker's "real-time" copying collector from 1978 [2], although Pauseless uses tags corresponding to various interesting states (marked/unmarked, forwarded/unforwarded) rather than just from-space/to-space.

[2] https://plover.com/~mjd/misc/hbaker-archive/RealTimeGC.html