There’s a Haiku review at Ars Technica.
There are plenty of comments - one mentions some multiuser code for BeOS that might be handy to find:
“Digger reply Jul 4, 2017 12:00 PM
Pointless trivia, there was a Japanese ‘school’ that used BeOS for teaching computing principles (or something, the site was in Japanese, so it was hard to tell for me) AND they’d written a multi-user login for it (and had screenshots) which I thought was brilliant at the time as one of the complaints (and rightfully so) against BeOS was the single-user only workspace.”