The server that hosts the appinventor.pevest.com virtual server suffered an outage late on January 17th, continuing into early January 18th. The Internet Service Provider that hosts the server has restored service. From their note to me, it seems there may have been a denial of service attack on their infrastructure.
I was in the midst of writing a new tutorial on creating “pretty user interface” components in App Inventor; that tutorial was lost in the outage. Not as bad as it sounds as the code and illustrations were all saved – I just need to rewrite the text.