PACK rats, shopaholic showoffs and avid collectors take note: the Internet will give you a place to track your stuff for free. One condition: you have to keep your wallet open.

The obvious question is, how many people would be bothered to catalog all their stuff, online or off? The answer, surprisingly enough, is millions. Whether there are enough of them to make a long-term business out of it, though, is anyone’s guess.

“The others have a challenge ahead of them,” said Randy Giusto, an analyst with IDC, a technology consultancy. “Zebo has been able to tap into the community feel that MySpace and others have evolved.” An offshoot of an online advertising technology company in San Francisco called Zedo, Zebo has so far appealed mainly to a younger crowd that uses its personal belongings as a social lubricant of sorts. Users post personal pages, à la MySpace, featuring lists of important items they own or want to own, and links to friends’ Zebo pages. Unlike MyThings and iTaggit, which use technology or site experts to help users determine the value of their items, Zebo’s users estimate their own net worth.

Roy de Souza, the chief executive of both Zebo and Zedo, said the site, which ended its testing phase in September, is focused on helping users shop together rather than helping individuals manage items they own, as its competitors do.

So far, Mr. de Souza said, the site has not earned a profit, mainly because it has not yet built systems to capitalize on its users’ consumerism. Zebo will in the coming months include more ways for retailers to, say, pitch cameras to Kim E and others who advertise their wish lists on the site.

In the quest to persuade people to post items they own, MyThings has a different solution, according to Martha Danly, the company’s chief marketing officer. In addition to allowing people to record items manually, the company is lobbying online retailers to automatically log purchases on MyThings, with the permission of members.

Ms. Danly said retailers and manufacturers who register purchases with MyThings on behalf of its customers will earn the right to advertise related items to those customers whenever they visit their MyThings pages. The site retrieves warranty information and product specifications when someone logs in an item, saving that information on their MyThings page.

Ms. Danly said this approach can spare users the need to record serial numbers and purchase records. “It’s essentially a digital shoe box of the things you’re buying, which is important if you have a warranty claim or it’s stolen,” she said.

Like its competitors, MyThings allows people to post lists of possessions privately, with only user names associated with their collections. The company passes on user names only to retailers who log purchases into the site.

MyThings is an outgrowth of an online service called Trace.com, introduced in late 2004 as a way to help people track down lost or stolen valuables, like fine art and antiques, or looted Nazi-era art. That site, which still operates, is working with law enforcement officials to build a central database of stolen goods so that auction houses, pawn shops and other businesses may determine the legitimate ownership of items they sell, and report stolen property.

Items registered with MyThings, Ms. Danly said, are automatically registered with Trace.com, so if users lose those goods, pawnbrokers or others can alert the owners and law enforcement agents.

Accel Partners, which backed Facebook among others, and Carmel Ventures, a venture capital firm specializing in software companies, pumped $8 million into MyThings a year ago. Earning back that money will take time; Ms. Danly said the company will begin running ads this summer, at the earliest.

In a sense, Mr. Altounian’s constituencies bridge those of Zebo and MyThings. Satisfying both groups “is a really big challenge,” he said, and involves embracing the evangelism of those who will post their iTaggit CD collections on their MySpace pages, while also serving more serious collectors with sophisticated cataloging and tools.

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