These apps have support for huge amount of printers and allow printing over Wi-Fi, Bluetooth, and most importantly, USB.
It seems they might be based on some existing project, though. They all have very similar UI, and function the same.
Printer2Go and PrintHand don’t just have similar UI, but exactly the same UI.
@user224 Well, there is a print utility on @fdroidorg and a (quite oitdated) lort of #CUPS.
Needless to say basically all decent printers should offer Print-from-Mail, Print-from-USB, Print-from-SMB & Print-From-PDF and literally support just sending a PDF file to it.