Boomaga (BOOklet MAnager) is a virtual printer for viewing a document
before printing it out using the physical printer.
The program is very simple to work with. Running any program, click
"print" and select "Boomaga" to see in several seconds (CUPS takes some
time to respond) the Boomaga window open.
If you print out one more document, it gets added to the previous one,
and you can also print them out as one.
Regardless of whether your printer supports duplex printing or not, you
would be able to easily print on both sides of the sheet.