Routine maintenance in our hosting yesterday evening (2015/08/12) caused a lengthy downtime of the server our website is running on. Although the server itself was operational right after the maintenance, there were some network issues, causing the server not to be reachable from the outside.
In the meantime, the issue has been resolved.
UPDATE (2015/08/14): the same issue also caused problems with e-mail, which was not resolved until yesterday (2015/08/13) late in the evening. Any communication through the contacts or comments form will not have arrived and will have to contact us again.