PHP is a open source language. It will easily available on internet, we have to just plug and play. It can be easily installed and developed on different platforms like: Windows, Linux etc.
Joomla is a open source content management framework (CMF) for publishing content on the World Wide Web and intranets and a MVC web framework that can also be used independently.
CodeIgniter is an open source web application framework, for use in building dynamic websites with PHP. CodeIgniter is loosely based on the popular Model-View-Controller development pattern.
Fuel your application with high performance deriving from smart and efficient database development and optimization.
WordPress is a free and open source blogging tool and CMS based on PHP and MySQL. It has many features including a plug-in architecture and a template system.
OsCommerce ("open source Commerce") is an e-commerce and online store-management software program. It can be used on any web server that has PHP and MySQL installed.
Yii is an open source, object-oriented, component-based php web application framework. Yii is also based on the popular Model-View-Controller development pattern.
There are many of payment gatway available in market but PayPal is very fast, easy, secure method to transfer currency from buyer to seller. And it will provide all international currency.