Is there a list of the operating systems for which the Parrot virtual machine can be built? I would rather not go through the release notes of every version to figure it out.
A better question is, which operating systems are you interested in?
We used to keep a PLATFORMS document up-to-date, but it hasn't seen much love lately:
https://github.com/parrot/parrot/blob/master/PLATFORMS
In general, Parrot runs on Linux, FreeBSD, OpenBSD, NetBSD, Solaris, OS X, Windows, RTEMS and a few other esoteric operating systems.