As noted in a tip from TUAW reader Barry T., attempts to view the Now Software website are now redirected to a Google Sites page. On that page, there's a link to information about the current state of the company. That's where this letter from Now's John Wallace explains what killed the company (click the Read More link to view the letter):
The Google Sites pages provide access to the user forums and other help-related information from the old Now Software website.
Update: Several readers have noted that BusyMac, the company that develops and sells BusyCal and BusySync, was founded in 2007 by Dave Riggle and John Chaffee. The two developers were among the brains behind Now Up-To-Date, and left about the time NightHawk was just starting development.