It turns out that I started the procstat command before the Big Gap, but didn't finish it. It didn't actually work and was just a placeholder. So I've made it do things.
It's not a complete clone of the FreeBSD one, but it doesn't set out to be (It has a different output format and because of that post-processing can be done with shell scripting and ordinary tools like awk.), and some of what the FreeBSD one does isn't cross-platform anyway.
http://jdebp.info/Softwares/nosh/guide/commands/procstat.xml