Since the 1830s, barter in some western market economies has been aided by exchanges which use alternative currencies based on the labour theory of value, and which are intended to prevent profit-taking by intermediaries. Examples include the Owenite socialists, the Cincinnati Time store, and more recently[when?] Ithaca HOURS (time banking) and the LETS system.

It's a little awkward, so we'll get straight to the point: This Tuesday we humbly ask you to defend Wikipedia's independence. We depend on donations averaging about $15, but 99% of our readers don't give. If everyone reading this gave $3, we could keep Wikipedia thriving for years to come. The price of your Tuesday coffee is all we need. When we made Wikipedia a non-profit, people warned us we'd regret it. But if Wikipedia became commercial, it would be a great loss to the world. Wikipedia is a place to learn, not a place for advertising. It unites all of us who love knowledge: contributors, readers and the donors who keep us thriving. The heart and soul of Wikipedia is a community of people working to bring you unlimited access to reliable, neutral information. Please take a minute to help us keep Wikipedia growing. Thank you.

While some people may balk at an online community for finding babysitters, I know several parents who say it’s actually very difficult to find a sitter they can trust. BabysitterExchange started in 2000 as a babysitting co-op, and it has since expanded to the point that members use it to reserve time when they just have some errands run, need help tutoring their kids, or want a temporary house-sitter.