It’s the latest ion a series of moves to expand the eBay developer community. Last summer, the company opened up a collaborative website, the eBay Community Codebase, to provide a hosted project developer site for anyone willing to open source their code.

Applications developed by third parties, in effect, extend the eBay brand to other channels and marketplaces. It’s similar to programs already in place at Amazon, which offers web services hooks so third parties can embed the Amazon engine in their own commerce sites.

When it opened its developers program, eBay set charges because it wanted to ensure that developers used its resources efficiently, because each application developed ultimately executes on the eBay infrastructure.

Its now-discontinued fee schedule ranged from $1.25 to $2.90 per thousand calls to the eBay engine, and annual membership fees ranging from $500 to $5,000.

Free access is not commonplace, claimed an eBay spokesman, who noted that other aggregator sites might offer limited free programs, such as specifying a ceiling to the number of no-charge transactions, or limit free access to non-commercial use.

For instance, that’s what the Amazon search subsidiary Alexa Internet Services does. It charges $0.00015 for each hit to the search engine beyond the 10,000-free transaction per month threshold.

However, by contrast, Amazon does not charge for use of web services interfaces to its core merchant site. Instead, it incentives such as customer referral commissions. Amazon boasts that over 120,000 developers have registered for its web service program since it was launched in July 2002.

Consequently, eBay has taken the hint, and is throwing off charges to spur adoption. Over the past year, the eBay developer network has more than doubled to roughly 20,000, accounting for 22% of listings on the site.

In another announcement, eBay announced a developers challenge contest that will award prizes for best individual application and best collaborative open source applications. Winners could get $5000, Xbox 360s, or iPod Nanos, plus an all-expenses paid trip to demonstrate their app at the 2006 O’Reilly Emerging Technologies Conference.