Imagine receiving a pair of handmade sea monster arms in the mail: long, green, covered in suction cups. Danielle Athanas was understandably surprised, then delighted.

"When I opened the box, my first reaction was, 'What am I going to do with these?' Then I thought, 'Oh! Now I have a Halloween costume - I haven't dressed up for Halloween in years!'" says Athanas, who received the costume accessories along with a box of other ocean-themed goodies as part of an online craft swap.

At a time when Web sites like etsy.com have created a booming marketplace for those looking to buy or sell handmade items online, other crafters are fueling another trend: swapping their goods with strangers.

"I love to craft and I hate keeping stuff. When I make something and I keep it, I tend to look at all the things I could've done better. So I like to give things away," says Athanas. "And the other thing for me is, it's really cool when I stop and think about it that stuff that I made is all over the country. … Little old me, I sit and crotchet in front of my TV, and my stuff is all over the place."

Athanas, 27, of Salem, N.H., has completed seven swaps since March and has three in progress. Her favorite place to sign up is Craftster.org, where swaps range from embroidered tea towels to "pagan, wiccan or witchcraft-related" items. Most call for completed items, but some involve swapping fabric or crafting supplies.

At Swap-bot.com, a site devoted exclusively to swaps, the most popular ones tend to involve artist trading cards - small works of art that let participants share their artistic styles with others. At any given time, the site features 500 active swaps, and it has hosted more than 20,000 since 2005.

Swap-bot uses a computer algorithm to mix up participants and assign partners, sends out reminder e-mails to participants, and includes a feedback system to deter "flakers" or cheaters who don't send their packages.

But why go through the trouble of making something for someone you don't know?

"I think the No. 1 thing is that the lure of getting a package in the mail is pretty strong," says Rachel Johnson, 27, of Eugene, Ore., who founded the site with her husband. "But I like to think it's also a way of connecting physically with someone you only know as a screen name. People are meeting and connecting with people from different countries and different cultures."

Jenna Zeidler, who posts links to every craft swap she can find on her blog, swapdex.blogspot.com, agrees. She sees craft swaps as part of the larger resurgence of handmade goods.

"When you swap a handmade item, it's like you're getting a relationship with the person that made it because you made something for them and they made something for you," she says. "As there's been this revival of handmade over the mass produced, I think people want more of a connection with the item and with the creator of the item."

Zeidler, 27, of Champaign, estimates she has completed 150 swaps in the last seven years. Many of the early swaps were art-focused (she remembers getting some "weird molten glass sculptures" in one swap), but the trend recently has been toward making functional items, such as tea towels or aprons.

Zeidler has posted links to about 400 swaps in the year since she started her site.

"There's a couple different sites where there are lots of swaps hosted on the same site, but there are a lot of swaps where someone on their blog will just say that they're hosting an apron swap or quilt square swap, and unless you read their blog, it's really hard to find them," she says.

"In my normal job, I work in a corporate library for a software company, so I'm very adept at setting up alerts efficiently and researching," Zeidler said. "So I thought, 'I'm doing all this work, I might as well put it out there for everybody."'

The only downside is the potential for flaking, she said, but in most organized swaps, other participants dubbed "angels" will fill in and send a package. Aside from two or three swaps where it was clear her partner put little effort into the project, she has no complaints about what she has received.

"On the whole, I have always been delighted when I get a package in the mail," she said.