http://www.simplexrepaginator.com/
Ingests PDF files of double-sided (duplex) documents scanned with a single-sided (simplex) scanner. Output is a corresponding PDF that has been "repaginated" so that the front and back pages of each paper sheet are in the correct order.
Scanning a stack of paper sheets, first face-up and then face-down, results in a logical page ordering such as this: 1,3,5,7,8,6,4,2. This project will ingest that PDF file and produce one whose pages are in the logical order 1,2,3,4,5,6,7,8.
Primary purpose is enable batch scanning of household files using inexpensive simplex document-feeder scanners.