Works in portrait and landscape orientation, can read inverted codes, is Material Design and doesn't do anything else but decoding a barcode.

Uses the ZXing ("Zebra Crossing") barcode scanning library. Supported barcode formats are: AZTEC, CODABAR, CODE 39, CODE 93, CODE 128, DATA MATRIX, EAN 8, EAN 13, ITF, MAXICODE, PDF417, QR CODE, RSS 14, RSS EXPANDED, UPC A, UPC E and UPC EAN EXTENSION.

This is open source:
https://github.com/markusfisch/BinaryEye