If there is, I'd like to find it. A friend and coworker's garage would flood when it rains, so he hired someone to build a drainage trench to deal with it. The guy he hired started the job, found out that my friend built web sites and asked if they could trade the trench for a site. My friend got the trench, plus a new deck for the backyard in exchange for the site.

I have used http://www.techscratch.com/ for some help with graphics and design stuff. Its not exactly this, its mostly for small tasks (1 - 5 hours) and you get points that you can then spend to get tasks done.

There is something around here in the Bay Area called the BACE time bank. BACE is Bay Area Community Exchange: http://timebank.sfbace.org/

The code it uses is a fork of oscommerce.

None that I know of. But if you find one, I advise you to bear in mind that in the United States, barter transactions are generally taxable:

http://www.irs.gov/taxtopics/tc420.html

I'm fine with that, but I like the idea of transactions which bypass the banking system. If I can avoid giving my money to financial middlemen, then why not?