osCommerce is an Open Source based online shop e-commerce solution that is available for free under the GNU General Public License. It features a rich set of out-of-the-box online shopping cart functionality that allows store owners to setup, run, and maintain their online stores with minimum effort and with no costs, fees, or limitations involved. - 
OSCommerce

Zen Cartâ„¢ truly is the art of e-commerce; a free, user-friendly, open source shopping cart system. The software is being developed by group of like-minded shop owners, programmers, designers, and consultants that think e-commerce could be and should be done differently. - 
Zen Art

phpShop is a PHP-powered shopping cart application. It is released under the GNU General Public License. The primary purpose of phpShop is to provide a simple shopping cart solution that is easy to customize to suit any purpose. phpShop has less features that many other shopping cart applications, but is generally easier to customize. All that is required to effectively customize phpShop is a basic knowledge of HTML, PHP, and SQL. - 
phpShop

Shopping cart script for sellers of intangible goods. What is intangible goods? Well, like software, ebook and so on. So if you are a seller of digital software downloads or some weight-loss ebook, then this shopping cart might be useful to you. They provide such features and "buy-now" buttons for eBay, Craigslist, MySpace and any more with integrated automated payment merchants. Nothing could be easier, just copy and pay those buttons. Furthermore, their shopping cart is able to calculate taxes and shipping as well. The best thing, this service has unlimited bandwidth with no setup fee or transaction fees - just a monthly fixed fee.

Free search engine friendly eCommerce shopping cart, its enables you set up online shop basket powered website quickly. Easy to configure. boss cart, free ecommerce shopping cart, shopping basket software, online store, build ecommerce sites. - 
Boss Cart - Free Shopping Basket

iG Shop free ecommerce shopping cart helps you create your own online ecommerce stores very quickly and completely free of charge. ig shop, igeneric ecommerce shopping cart build online store with iGeneric shopping cart. - 
iGeneric Scripts

NetDirector e-Trade Pro is a feature rich, fast to deploy and easy to use sales-led e-commerce software solution. With no contract and only weekly payments, NetDirector offers a low financial risk option for companies looking to sell successfully. - 
G-Forces

Tradingeye is a web standards compliant shopping cart & CMS built from the ground up with web accessibility and SEO in mind. With the Tradingeye - Site & Shop Builder your e-commerce shop will be accessible to 9.1 million more accessibility impaired, home-bound shoppers than with rival e-commerce products. This opens the door to a demographic with an estimated spending power of over £50 Billion in the UK alone. - 
Tradingeye

It is surprising that most websites don't take SEO (Search Engine Optimization) seriously. Hence they are not found by most people surfing the web. I mean what do you usually do when you want to look for something on the web? You go to your favourite search engine and start searching for keywords or something right? You know Google? That is one of the more popular search engines out there. And there is where most people start. If you are planning to do some e-commerce, you should seriously consider improving on your SEO. However, sometimes it could be due to the script you are using. Most scripts are just not mean for SEO and they tend to create problems for search engine bots when they come "spider" your site. However, SEO Toaster is a ecommerce script especially designed with SEO in mind. Yes, right out of the box. You don't have to worry about adding this plugin or that plugin or hiring some coder to improve on the script. And you don't have to worry about upgrading. It allows you to easily build ecommerce sites with just a few clicks and minimum web knowledge. Visit their website to find out more.

Automate your personal and business advertising! The software program makes the difficult CL posting process child's play and helps you manage your ads. GREAT FOR: Real Estate Professionals who want to list many properties in multiple locations and anyone wanting to maximize their exposure on Craigslist. Unlike most CL posters that simply do not work, this software is continually tested and updated and we offer a working demo! - 
CraigsList Auto Ad Poster

MerchantOS makes point of sale software easy. No software installation required. We'll keep your software running so you don't have to. 1. Faster, Easier Software Installation 2. Less Money Spent on IT 3. Less Money Spent on Computer Hardware 4. Better Cash Flow 5. Real Time Information for Multi Store Solutions 6. Improved Inventory Control 7. Easier In-Store Operations and Customer Service 8. Improved Sales 9. Off-Site Access 10. Eliminates Workstation and Operating System Concerns - 
Merchant OS

Completely customize your website with industry-leading software and plug-ins that enable you to launch your entire product inventory online at an affordable price - 
StoresOnlinePro

We are a product development company with immense experience in the entire software life cycle of software product and custom application development. We are a UK registered company based in London, UK. We will help you to succeed in your online business by giving you the right product and by being with you, helping you, mentoring and training you in every step to make your online business a huge success. Our focus is and always will be to help you “to sell More online and to improve your financial bottom line”. - 
RiteCart