Option menu opened
(Don't worry - you don't need them all, but everything is tunable, just in case)

Opened log right after startup

PStill can combine mutliple input files into one PDF (even as mixed set)
Just drag several input files on the GPStill main window...

Selecting a N-UP script to place 4 page on 1 in the result

Result of the application of the 4-on-1 option
Sample document was a PS file from the arXiv.org e-Print archive