The minimal no-fuss online free QR code creator is simple free and adequate. There is are python libraries PyQRCode and qrcode. There are various subscription services, but they are remarkably expensive and so not recommended. If I want fancy tracking of clickthroughs on QR-coded links, I could use bit.ly or some other URL shortener/tracker.
QR codes are additionally supported quietly in lots of software; for eexample, QR codes are one of the barcode formats suported by DTP package scribus.