Before you resort to relying on strangers for those extra lawn chairs or sewing machine, ask your own network. Talk to family, friends and coworkers. If you don't know your neighbors, this makes for a good excuse to introduce yourself.
If you opt to go the online route, pull in other people with you to create a borrowing network you trust. ShareSomeSugar.com, NeighborGoods.net, Frenting.com and ThingLoop.com all let users pull together a network using email contacts. You can also find people who live in your zip code.
It can be an informal contract, but clearly communicate your expectations as a lender or borrower. Discuss time frame, care of the item and liability if something happens to it. Use free tracking site ReturnMyPants.com to keep tabs.
Although the sites themselves are free, lenders may require borrowers to make a security deposit before walking away with a potentially valuable item. BorrowingCircle.com charges late fees of 10 cents per day for books and 20 cents per day for movies. Half of the collected fees go to the site, the rest to the item's lender.
Don't be a person who always borrows and never gives back. Borrowing sites thrive on an active community. If you like the idea, be prepared to list an item or two to lend. If you don't have anything to lend in return to a borrowing partner, at least follow up with a handwritten thank-you card.