Over the past 15 years, the Internet has transformed society. It has generated an entire industry, revolutionized commerce and altered the ways people communicate, connect and build relationships.

From a commercial perspective, online shopping has generated a shift in consumer behavior. According to two studies by the Pew Research Center, this shift is far from over. In September 2010, 58% of Americans went online for information about products to buy, up from 49% six years earlier.

The six companies profiled here are building strong momentum in the realm of online shopping. Their technologies can help consumers save time and money, but the websites also do something else: They expose people to new strategies for acquiring, selling or trading consumer goods. Plus, they plug in consumers to the new currents that will inevitably follow as technology continues to transform personal transactions of all kinds.

thredUP

Based in San Francisco, thredUP is an online clothing swap. Parents can exchange used clothes, as well as books and toys. The website bills itself as a time-saving solution for busy, thrifty parents. You don't have to rummage through garage sales, and the inventory is more abundant than what you'd encounter at the thrift store.

In the real world, clothing swaps are few and far between because they are time-consuming and difficult to organize. ThredUP's marketplace streamlines everything into one browser-friendly interface.

For basic swaps, thredUP customers pay $5 plus $10.95 in shipping fees.

ModCloth.com

ModCloth.com is a boutique-style online retailer that chooses small lots from a variety of designers, all retro in style. ModCloth features only a few of each item in each individual size, enhancing the uniqueness of its shopping experience.

In the real world, boutiques can be expensive and difficult places to shop because they tend to run out of inventory quickly. As a solution to this problem, ModCloth provides an extensive inventory of department-store alternatives.

Above all, the company engages in strong social-media efforts to engage its customers. Site browsers can vote on items that they'd like ModCloth to buy and sell.

The site transforms shopping by presenting a holistic experience online, an accomplishment that eludes many virtual retailers.

Etsy

Established in 2005, Etsy has gained a reputation as one of the world's strongest marketplaces for handmade creations. Its network provides people a place to sell their handcrafted clothing, jewelry, furniture, toys and other items.

Anyone with a handmade product can create a store on Etsy, and everyone can shop there. Brooklyn-based Etsy aims to foster a do-it-yourself culture. It periodically brings online users together for real-world social events that have nothing to do with commerce. Participants show up to learn new skills and socialize.

Lifesta

Lifesta is a marketplace for people to buy and sell daily deals picked up from sites like Groupon and LivingSocial, which bring out the "impulse shopper" in everyone with great face-value offers.

On Lifesta you can buy deals you missed, look for deals that might hold appeal or sell any deal you bought and won't use.

The site offers a way out for shoppers who may have been too eager in snapping up a great deal at Groupon for, say, a morning yoga class. Rather than be stuck with a voucher you'll never redeem, you can offer it on Lifesta at whatever price you choose. Lifesta gets its cut -- 99 cents plus 8% of the sales price -- and you get all or some of your money back.

Rehash

Rehash is another online community for trading clothes and books. The goal of the site is to provide a space for people to share items that would otherwise cost money or go to waste.

The majority of items in Rehash's database are secondhand, but items are typical of what a shopper would find in a mall. Products found on Rehash include Banana Republic tops, trendy ankle boots and Hollister T-shirts.

Rehash is owned by Orpheux Design, a Florida Web studio and creative agency.

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Friendgiftr

Remember Facebook gifts? They were really fun and thoughtful -- until people realized that they weren't actually real.

Rob Carpenter decided to take Facebook gifts to the next level. In 2008, he established Friendgiftr, a business he has described as the world's first social-media and mobile-based e-commerce 2.0 company. Now, you can send real gift cards from about 150 merchants. Its apps aim to commercialize social networking sites and smartphones.