Players use third party tools at their own risk. For a full list of third-party tools, see this category list.
For official rules and regulations regarding the use and acceptable functionality of third-party tools, see this page.
arrBay is a website that develops trade between players by allowing them to post items for sale and read posts that other pirates have published. It is a quick easy way to get the word out that you are selling that war brig, and to get the price you're asking.