From the website (links mine)...
CraigNewmark?? observed people on the Net, on TheWell and in UseNet, helping one another out. In early '95, he decided to help out, in a very small way, telling people about cool events around San Francisco like the Anon Salon and Joe's Digital Diner. It spread through word of mouth, and became large enough to demand the use of a list server, majordomo, which required a name. [...] Over time, people started posting items on the list in different areas, jobs, stuff for sale, and apartments, the latter in response to San Francisco's apartment shortage. Craig wrote software which could automatically add email postings to a site which became www.craigslist.org. [...]What works
Giving people a voice A sense of trust and even intimacy Consistency of down-to-earth values Simplicity No charges, except for job postings Freshness of the material No ads, particularly no banner ads
craigslist won the 2001 WebbyAward?? for best OnlineCommunity.