I am trying to determine if there are any free and/or open source projects that are similar to the freelance website Guru.com. Basically, I need a system where users can post a "wanted ad", which other users will then place bids on. Additionally, I'd also like users to be able to post a "services offered" ad, which other users can then purchase for a set price. I am having very little success trying to research this on my own, since I don't know if there is a name for this type of software or not. If such software does exist, can someone point me in the right direction? Even just a name I can use to refer to this type of software so I can start doing research on my own would be sufficient. Thanks for any help!