I always thought it was an In-House development (by Nicolas H.), but while I was looking for something different I came across this press release through google: Virtools and RTIME announce development and marketing partnership
RTIME was then aquired by Sony and renamed to SCE-RT. Same tech was added in 1999 to shockwave
P.S update from 2006.06.23
At the end Virtools dropped the approach of using 3rd party tech and Nicolas and Julien, from Virtools, developed all the technology found in the MultiUser Pack.
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