eBay is now officially beta testing its subscription-based Selling Manager service as a platform for third-party developers to sell their embedded tools.

The space is used by close to 300,000 online merchants to manage their businesses at my.ebay.com. They have now become the target of this new campaign hoping to sell them software to manage their shipping, accounting, customer relationships, market research and inventory management on eBay.

As an incentive to third-party ISVs the company has stopped charging admission to Selling Manager like it used to.

According to eBay's count, some 87,000 third-party developers have built more than 13,000 live applications over the years that consume its Web Services. And eBay says 60% of all its listings come through eBay Web Services and more than a third of all listings on eBay are placed through a third-party app - an increasing important number given the luster fading from the eBay star.

Beaten down by Amazon and other big e-commerce retail sites and facing long-term challenges, eBay traffic dropped over the holidays; it reported a 16% plunge in Q4 revenues for its marketplace business, which represents about half its annual revenues; overall revenues declined 7% with profits off 31%.

eBay is now refocusing on used and overstocked goods and collectibles. Its other hopes are PayPal, which it's using for Selling Manager, and, if lucky, Skype, which it overvalued when it bought it for $2.6 billion in cash and stock back in 2005. Skype, which is doing $550 million a year, is currently looking for SMB corporate customers. If that doesn't work eBay may have to sell it.

The Selling Manager beta, the result of a pilot eBay kicked off last June, is supposed to make it easier for eBay sellers to find and subscribe to the tools they need.

UPS, for instance, is the first carrier on the beta platform and is integrating its Worldship software so sellers can manage their shipping from inside my.ebay.

Applications have to be approved by eBay, which wants a kickback on any subscription-produced revenues.

The next-generation APIs that eBay is using for e-commerce are based on the open standard gadgets specification defined in OpenSocial.

eBay first opened its APIs in late 2000. According to Kumar Kandaswamy, senior manager of eBay Developers Program, there are some 200 APIs end-to-end.

eBay rolls new code every two weeks and sometimes that adds up to six million lines of code.

The flea market site claims 83 million active users and around 112 million listings worldwide at any given time. It figures sales work out to $2,039 a second.