Sass - Syntatically Awesome Style Sheets
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
PostCSS - Increase code readability. Add vendor prefixes to CSS rules using values from Can I Use. Autoprefixer will use the data based on current browser popularity and property support to apply prefixes for you.
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.
Stylus - EXPRESSIVE, DYNAMIC, ROBUST CSS
Braintree - An all-in-one solution to accept, process, and split payments in your mobile app or online - from small business to large enterprise.