A free program for Android, by Twinangels.

QR WiFi Connect allows you to connect to WiFi quickly by scanning a pre-generated QR code. It supports WPA, WPA2, WEP, and other open networks. Simply point the rear camera of your device at the QR code, and the app will automatically connect you to the scanned network.

This application can also display the password of the WiFi network once scanned. Moreover,  all scanned networks can also be saved in the history section.

Tip: You can generate a QR cd with your wifi data by using one of the many online generator tools. However, ensure that the QR code is valid and contains the correct SSID and password.