Sharetribe - Build your online marketplace business. You don't need a developer.
RetailMenot - The RetailMeNot mobile app allows you to find deals on the go for both online shopping and in store shopping.
Shopify - Shopify is a powerful ecommerce platform that includes everything you need to create an online store and sell online. Try it free for 14 days.
Slickdeals.net - Slickdeals: The Best Deals, Coupons & Discounts on everything
Arcadier - Build an online marketplace in minutes, no coding required.
Honey - Honey is a browser extension that automatically finds and applies coupon codes at checkout with a single click.