Having implemented several PHP-based ecommerce projects in recent years, I can attest to the importance of selecting an implementation platform which meshes well with your project goals and team skill set. Literally hundreds of open source and commercial PHP-based ecommerce solutions exist, yet only a select few will adequately meet the aforementioned requirements. If you're currently exploring a PHP-based ecommerce project, consider starting your investigations by learning more about these five prominent solutions.

PHP Ecommerce Solution #1: Magento

Magento is without a doubt the 800-lb gorilla in this selection of projects, having recently been acquired by eBay. Built atop the Zend Framework, Magento's adoption has skyrocketed in recent years, having amassed a community of more than 100,000 deployments, including globally recognized companies such as OfficeMax, Twentieth Century Fox, and The North Face (see the Magento showcase for a list of prominent users).
In addition to the appealing technological foundation, Magento users can participate in a thriving community, which among other resources offers a hyperactive forum and vast extension marketplace. These resources offers developers access to almost 6,000 free and commercial extensions. Among other extensions you'll find solutions for PeachTree and FreshBooks integration, a wide variety of templates including some that are useful for clothing- and watch-oriented websites, and an extension capable of producing a mobile version of your store.
Like many successful open source-oriented companies, Magento relies on a hybrid licensing model, offering a variety of editions including a free community version (Magento Community) and two paid versions (Magento Professional and Magento Enterprise).
Be sure to check out the official Magento demo to obtain a hands-on understanding of both the front- and back-end interfaces. Additionally, if autonomously building and maintaining a custom Magento store isn't possible, consider checking out Magento go, a turnkey solution for building your own store without having to write a single line of code.

PHP Ecommerce Solution #2: LemonStand

LemonStand is another very capable solution which although lesser-known than Magento has nonetheless managed to assemble quite an impressive customer list, counting among its users UNICEF and edgeware.
Based on my perusal of the official demo, perhaps LemonStand's most noticeable feature is the slick administration interface. A well-organized dashboard provides a variety of useful statistics pertinent to traffic and sales. Users have the option of additionally accessing Google Analytics-specific data. The product management interface is equally impressive, giving users a simple set of forms for managing all aspects of each product, including the description, images, price, page layout, shipping options, and much more.
Like Magento, LemonStand supports quite a few different leading payment gateways, among them PayPal, Authorize.Net, PSIGate and First Data.
LemonStand does not offer a free version, but a commercial license costs just $299.98 Canadian ($307 US based on the June 7 exchange rate). You can download a fully-functional copy for experimental purposes by downloading a free developer license, and additionally can take LemonStand for a test-drive via its official demo.

PHP Ecommerce Solution #3: osCommerce

osCommerce is almost certainly the pioneering ecommerce project within the PHP community, having been launched in 2000 by developer Harald Ponce de Leon. An open source project, the osCommerce website points to almost 13,000 live osCommerce-driven online stores and a community of almost 250,000 members as evidence of the project's success.
Like the aforementioned projects, osCommerce sports a vast set of features, including powerful catalog, shipping, and taxation management capabilities. It also supports numerous payment gateways, among them PayPal and 2Checkout.com. Additionally, you'll find quite a few high-profile adoptees, including the Ubuntu Shop.
Perhaps a result of the project's age, osCommerce is lacking in a few areas which have become increasingly important in recent years. Notably, the documentation is woefully scant as compared to the aforementioned solutions, as is the availability of community resources. To be fair, osCommerce is an open source project and it lacks the considerable resources available to commercial solutions. However, these drawbacks are nonetheless worth pointing out as they are likely to quickly become sources of frustration among less experienced developers.

PHP Ecommerce Solution #4: PrestaShop

PrestaShop is the youngest solution of the five introduced in this article, with version 1.0 having been released just under 3 years ago (at the time of this writing). Over this relatively brief period, both PrestaShop development and worldwide adoption has continued at a rapid pace, with version 1.4 adding an impressive 65 new features and more than 50,000 shops having been created since the project's inception. The hard work was acknowledged with the project winning Packt Publishing's coveted 2010 open source award for ecommerce.
Like Magento, PrestaShop has created an active extensions marketplace, with more than 700 free and commercial modules available at the time of this writing. Additionally you'll find more than 700 templates useful for theming your store in accordance with every imaginable commercial sector.
PrestaShop is open source software, published under the Open Software License. You can download the latest version from the PrestaShop website. Also, be sure to check out the official demo.

PHP Ecommerce Solution #5: UberCart

All of the solutions described thus far are standalone, meaning that nothing else generally needs to be installed except for the LAMP stack. However, because so many websites run on content management systems such as Drupal, I thought it would be useful to conclude this article with at least one bit of insight into a popular CMS module named UberCart .
UberCart is one of Drupal's most popular modules, with more than 30,000 websites using this combination to power their ecommerce operation. The advantages of doing so are many, including the notable ability to use UberCart in conjunction with the rest of the Drupal module ecosystem. Special effort has been put into product distribution capabilities, which go beyond shipping physical products, as UberCart can also sell downloadable products such as ebooks and even products comprising a virtual economy.
UberCart is an open source project released under the GPL 2.0 license. Be sure to check out the official demo to obtain a feel for UberCart's interface.

About the Author

Jason Gilmore is founder of the publishing, training, and consulting firm WJGilmore.com. He is the author of several popular books "Easy PHP Websites with the Zend Framework", "Easy PayPal with PHP", and "Beginning PHP and MySQL, Fourth Edition". Follow him on Twitter at @wjgilmore.