WooCommerce - A freely available eCommerce plugin that enables shop facilities on your WordPress website. Functionality enabling extensions & beautiful themes available.
Pilgrim SDK by Foursquare - Location data to understand & engage with your customers
Thirty Bees - Open e-commerce platform designed to work out of the box.
Stripe iOS SDK - Accept both Apple Pay and credit card payments easily on iOS
Squarify.io - Sync inventory between Square and Shopify.
MightySignal Top SDKs - Most used SDKs in top 200 free iOS apps. Learn what to use.