I don't know why I didn't find this until now, but Scott Kearney has written a PeopleSoft module for PowerShell. I haven't tried it yet, but it looks pretty good. You can do all of the usual psadmin.exe tasks, like starting and stopping app server, process scheduler, and web server domains, and several other tasks. It could be a real time-saver.
It looks like it hasn't been updated in a few years. It was targeted at PeopleTools 8.53, but likely works with other versions as well. It's apparently largely made up of calls to psadmin.exe, and how much does psadmin.exe change from version to version? Not all that much.
I should also mention psadmin-plus, a similar tool written in Ruby. It's being actively developed, and is from the same folks that bring you the PS Admin podcast.
