QR.io - Generate fully customized QR Codes, with color shape & logo
Eventbrite - Discover Great Events or Create Your Own & Sell Tickets
VisualCode - QR codes for everything
Attendize Event Ticketing - Attendize is a free & open-source ticket selling and event management platform
Uniqode - Uniqode: Revolutionizing QR Codes, Simplifying Solutions.
pretix - pretix helps you to sell tickets for your event in an easy way. It supports multi-lingual events and provides a wide range of features