AuctionIntelligence
AuctionIntelligence can help you:

• Better predict pricing of items on eBay.
• Know where and when to sell an item in order to maximize profit.
• Understand how to list your items in order to draw the most attention.
• Save search data indefinitely.
• Analyze eBay data over days, months, years.
• View charts of data to quickly visualize trends.

PPCalc - PayPal Fee Calculator
Allows you to quickly and easily determine what your PayPal fees would be if you were to receive a certain amount of money online.

It includes support for all the different PayPal fee rates and all the different countries and currencies that PayPal currently supports. You can also choose to calculate in the 2.5% currency conversion fee that is used in some multi-currency transactions.

You can also "reverse" calculate your PayPal fees to determine the exact amount a person must send you in order for you to get the amount you want.

They also provide a web based version at no charge.

PHPAuction
PHPAuction provides a complete suite of applications and services for building auction web sites. PHPAuction programs offer flexibility, power, and ease of use for small businesses and individuals. We can provide an integrated set of scripts that will assist in building successful web sites and increase business and sales.

PHP Pro Bid Auction Software
Ideally suited to Small-Medium Businesses PHP Pro Bid enables you to start up your very own eBay style web auction service. Installation is simple and takes a matter of minutes. You can control every aspect of the web-site via the PHP Pro Bid Admin control panel.

PHP Invoice
PHP Invoice is designed to automate your entire account, order, billing, ticket system needs. From displaying your sales content, to ordering, PHP Invoice will handle all your billing and authentication requirements with speed and ease.