SambaPOS - SambaPOS is an open source POS Software for Restaurants.
uniCenta oPOS - Award winning Point Of Sale
Odoo Point of Sale - Odoo is an online point of sale solution for retail and restaurants.
POSper - POSper is a Point Of Sale (POS) System with touch screen support designed for small businesses.
Floreant POS - Floreant POS :: Open Source Point of Sale – Think POS Think Floreant
Square for Retail - Point-of-sale app & set of tools for retail businesses