We check this website, now hypertextbook.com is up and dont blocked for our system and other users of the Internet.
So, answer to question: Is hypertextbook Down Right Now? - NO! hypertextbook is up!
If you have problem with access to site hypertextbook, and domain hypertextbook.com is not avalible.
Clear browser cache and/or try other web browser
(Chrome, Firefox or Safari).