PayPal - PayPal is the faster, safer way to pay online without sharing financial details, send and receive money or accept credit and debit cards as a seller
QuickMark - QuickMark makes everything possible.
Stripe - Online payment processing for internet businesses. Stripe is a suite of payment APIs that powers commerce for online businesses of all sizes. Use Stripe’s payment platform to accept and process payments online for easy-to-use commerce solutions.
ZXing - Barcode Scanner for Android
Braintree - An all-in-one solution to accept, process, and split payments in your mobile app or online - from small business to large enterprise.
Barcode & QR Code Scanner - A free app which allow to read and generate barcodes for Android.