PDFsam - PDFsam Basic, a free, open source, multi-platform software designed to split, merge, extract pages, mix and rotate PDF files
PDFTK Builder - PDFTK Builder is a free graphical interface to for PDFTK, making it much easier to use.
PDFill - Open, View, Edit, Save and Print PDF Documents without Adobe Acrobat
QPDF - QPDF is a command-line program that does structural, content-preserving transformations on PDF...
UnityPDF - UnityPDF lets you merge, split, divide, rotate, protect PDF files and more.
PyPDF2 - PyPDF2 - A utility to read and write pdfs with Python