bbPress.org

It’s possible to use it to power Classifieds like so (this is done with bbPress plus an adapted version of the Support Forum plugin together with the My Views plugins):

http://classifieds.weddingbee.com

However, as far as I know… it’s not currently easy to add all that meta info for each item – i.e. edition name, price, condition, etc. It’d be fairly straightforward to program a plugin to pull that off though! But it’s not currently available, as far as I’m aware…