When barter has appeared, it wasn’t as part of a purely barter economy, and money didn’t emerge from it—rather, it emerged from money. After Rome fell, for instance, Europeans used barter as a substitute for the Roman currency people had gotten used to. “In most of the cases we know about, [barter] takes place between people who are familiar with the use of money, but for one reason or another, don’t have a lot of it around,” explains David Graeber, an anthropology professor at the London School of Economics.

Check online swap markets and online auctions that have a bartering component such as Craigslist.com (check under "For Sale" for the Bartering category), Swapace.com, SwapThing.com, Barterquest.com, U-Exchange.com, Trashbank.com and Ourswaps.com. Check for local bartering clubs. Your local Chamber of Commerce may be able to provide you with information on similar clubs in your area.
While it may be free, there is no one monitoring the barter ads, so you must be aware of potential Craigslist scams, and realize that you are always at risk when it comes to meetups and exchanges. For example, about a year ago, I arranged to trade massage gift certificates for housecleaning. Since the individual was coming to my home, I was more nervous than usual. However, she offered good previous references, and we  arranged for a time to meet when my husband would be home, in case an odd, unexpected, or even dangerous situation arose.
During economic downturns, when there is a keenly felt shortage of jobs and cash, people have historically adopted barter systems. The world’s most established bartering-style system is Switzerland’s wir: the German word for “we” as well as the abbreviation of Wirtschaftsring, which translates loosely to “economic circle.” In 1934, the economy in Switzerland had tanked—as it had in much of the world. Two businessmen who were facing bankruptcy, Paul Enz and Werner Zimmermann, gathered 15 of their associates in Zurich and hashed out a solution: a mutual credit system.