Open ping servers, like Moreover Technologies' Weblogs.com, let other web services subscribe to a list of blogs that have recently pinged them. Blog search engines can provide fresh results very quickly by polling only the newly-updated blogs. Similarly, aggregators use results from ping servers to tell subscribers which items on their subscription lists have fresh material.
In addition to open ping servers, there are also proprietary ping servers that gather information only for their own applications. Most of the major blog search engines operate such ping servers.
Unlike open ping servers, proprietary servers with their own subscription applications have no incentive to share their received ping data directly with other servers, which may offer competing services. As these servers do not share their data, bloggers have to ping a large number of individual servers to receive the desired publicity. As a result, bloggers have turned to services such as Ping-o-matic and Pingler.com, which ping multiple proprietary ping servers and remove the need for website owners to accquire new servers to ping themselves.