At this time, "it is not known when or if we'll be able to get the site back online." That, according to the owner of www.historycommons.org. It's a technical issue. In the meantime, you can still use the site, and here are the obsessive compulsive ways I have figured out how to do so...

First, go to www.archive.org. In the "Wayback Machine" type in www.historycommons.org

Then it will bring up a "calendar" of dates the site was "memorized" in the "Wayback Machine."

Scrolling to February 2018, and clicking on that gives a link to this version of the site...

https://web.archive.org/web/20180224034530/http://historycommons.org/

The problem is, you can not use "Search" on that site. So, what I've been doing is I click on "Timelines" at the top left of the screen, and then I click on the "Complete 9/11 Timeline," and that brings you here...

https://web.archive.org/web/20180127011151/http://www.historycommons.org/project.jsp?project=911_project

Since I am EXTREMELY familiar with the timeline, this may be a little easier for me, BUT... what I do is I click on "View all events for this timeline (7194)." That takes you to here...