The host that provides all the primary services for the Wesnoth community, including forums, wiki, add-ons and the primary MP server, has been down for the last 4 hours. Work is underway to determine the causes and solve this problem as soon as it's possible. Stay tuned!
UPDATE 2010-07-31: the server went back online around 3:00 AM CEST. So far we still don't know the reasons for the crash, but we know that the server ran out of memory, which could have locked up the operating system indefinitely before being rebooted by hand.