This thing will generate a QR code from the supplied string. It is a native OpenSCAD program, so you don't need to download any third-party app to use it (once I figure out why Customizer keeps crashing on it).
Enter your string, set the minimum error correction level, choose a mask and away you go...
I've only got the data pre-set to generate QR codes up to version 6, which means there is a character limit of 134/106/74/58 (depending on your error correction level). I plan to add more so that you can generate larger QR codes.
I also plan to add the ability to set the size. It currently generates using 1x1x1 mm pixels.