As my sister comment mentions, ActiveState has some support for fork(). In my experience, only a few obscure things don't work.

But:

% perldoc perlfork
 ...
AUTHOR
       Support for concurrent interpreters and the fork() emulation wa
+s implemented by ActiveState, with funding from Microsoft Corporation
+.
       This document is authored and maintained by Gurusamy Sarathy <.
+.@activestate.com>.
 ...
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