I noticed that Curt Tilmes put out a new release of Proc-Wait3, which is just an interface for the wait3 function from <sys/wait.h>. Actually, I think wait3 and waitpid3 functions are candidates for core Perl.
Interestingly we have wait and waitpid, but there's no wait2 or waitpid2. Yet, we have wait3. Oh, and instead of waitpid3 we have....wait4.