Open Source Point of Sale is a web based point of sale application written in PHP using CodeIgniter framework. It uses MySQL as the data back end and has a Bootstrap 3 based user interface.
POS Application Open Source

Open Source Point of Sale is a web based point of sale system. The main features are:

Stock management (Items and Kits)
VAT, customer and multi tiers taxation
Sale register with transactions logging
Quotation and invoicing
Expenses logging
Receipt and invoice printing and/or emailing
Barcode generation and printing
Suppliers and Customers database
Multiuser with permission control
Reporting on sales, orders, expenses, inventory status
Receivings
Giftcard
Rewards
Restaurant tables
Messaging (SMS)
Multilanguage
Selectable Boostrap (Bootswatch) based UI theme
Mailchimp integration
reCAPTCHA to protect login page from brute force attacks
GDPR ready

The software is written in PHP language, it uses MySQL (or MariaDB) as data storage back-end and has a simple but intuitive user interface. The latest 3.x version is a complete overhaul of the original software. It is now based on Bootstrap 3 using Bootswatch themes, and still uses CodeIgniter 3 as framework. It also has improved functionality and security. Deployed to a Cloud it’s a SaaS (Software as a Service) solution.

LOGIN using

username: admin
password: pointofsale