PDFjam is a small collection of shell scripts which provide a simple
interface to some of the functionality of the excellent pdfpages package
(by Andreas Matthias) for pdfLaTeX.  At present the utilities available
are:

 + pdfnup, which allows PDF files to be "n-upped" in roughly the way
   that psnup does for PostScript files.

 + pdfjoin, which concatenates the pages of multiple PDF files together
   into a single file

 + pdf90, which rotates the pages of one or more PDF files through 90
   degrees (anti-clockwise).