Ping.fm is a free social networking and micro-blogging web service that enables users to post to multiple social networks simultaneously.

Making an update on Ping.fm pushes the update to a number of different social websites at once. This allows individuals using multiple social networks to update their status only once, without having to update it in all their social mediums individually. Ping.fm groups services into three categories – status updates, blogs, and micro-blogs – and updates can be sent to each group separately.

Ping.fm was created with the intent of making it as easy as possible to post updates to multiple social networking sites simultaneously. The idea came about when creators were updating status messages with micro-blogging sites Twitter and Tumblr. The idea of posting the exact same information in two places seemed a bit tedious, so Ping.fm was born.

(from wikipedia.org)

PingFM says this about their services:

We post your messages wherever you want!
That’s right, we support over 40 social networking sites and we’re adding more all the time.
Between our straight forward posting methods and advanced custom triggers, we make it easy for you to post your messages exactly where you want them to go.