Stripe: An API-based payment gateway solution that provides highly flexible solutions targeted at developers with a choice of multiple payments
Square: All-in-one payment both online and offline with no monthly fees and a simple point of sale
PayPal: A global third-party processor for e-business, which has multi-currency making it easy to interconnect with online merchants for international organizations
Authorize.Net: A payment gateway with features such as complete fraud control and features suitable to businesses with multiple payment types
Helcim: A fully transparent, competitive price structure with volume pricing, as well as, practical online and offline payment tools