The Newgrounds chat is a system where Newgrounds users can IM each other in a chat room. Before 2007, NG used an IRC chat client, but since the 2007 redesign, that was no longer officially used.
A new, official chat is in development by PsychoGoldfish and will utilise NG's usernames rather than the person making one up.
In 2010, the Newgrounds Radio Chat was used for the Chat link but was later removed by request of the owner.
The Radio Chat can be seen at http://www.newgrounds.com/portal/view/537101