A very old but finished timeline by Doug Hoff, already started in the glory days of the now non-existant soc.history.what-if discussion newsgroup (AH.com's precursor).
For whatever ASB reasons, humans never migrated to the Americas in prehistoric times. As a result, medieval explorers from the Old World - both from the West and East - find the New World to be a wilderness completely unaffected by man, still populated by many peculiar species of prehistoric megafauna. Meanwhile, in the Old World, the Mongol invasions of this timeline take on a different, more successful course… These two events contribute to reshaping the geopolitical, cultural and even technological landscape of the world in the following centuries. Creating a world both quite familiar, but also rather alien.
Empty America - Archived Version - Based on the Empty America archive thread created by board member Constantinople. Arranged into clickable chapters, and with some heading formatting, for greater ease of reading.
The thread was made in 2014, and reposted the timeline with materials given to Constantinople by its author, Doug Hoff himself, in the years before. (This thread was initially meant to collect the entire timeline in a more readable format, but Constantinople eventually made the other thread for it.)
Doug Hoff's original alternate history site, Althist.com - Doug's original site has been defunct since the late 2000s, this is a version archived at Archive.org, available via its WaybackMachine. The site includes at least some of the timeline (the author's largest by far), but probably nothing of the chapters written in later years.
In the late 2000s, you could also read the timeline in its entirety via links on this purpose-made blog by Doug Hoff himself. However, with even the Google groups incarnation of SHWI going under in the 2010s, the original posts with the timeline are now by and large inaccessible.
The AH.com discussions listed here are in chronological order, from the latest to the oldest.
Empty America: Discussion Area - For discussion of the AH.com-archived version. Constantinople also used it, aside from the other threads, to announce the posting of the full timeline, aided by Doug himself.
Empty America-Where can you find it now? - Brief old discussion, with some info on the recovery of Doug's site via archived form.
Empty America without the Emptiness - A discussion on a variation of the timeline's premise, with the variation being closer to OTL.
Old Board +/ Empty America - Discussion from the “wilderness years” of the timeline, when it was hard to access at all.
Continuing Empty America... - Very short old discussion on a potential AH.com continuation of the timeline. (As far as we know, no one has tried any sort of continuation project to date, though some have asked about that option. Also note that the TL wasn't completely finished yet at the time of that discussion.)
Empty America: What would have happened - Old discussion on the then most recent chapter of the timeline (the author wrote over a dozen more afterward).
[Alternate History] Empty America as a setting (RPG.net forums)
Glossary (Empty America) - An overview of alternate terminology and alternate geographic names in the timeline.
Prehistoric megafauna from the Americas that appears in the timeline:
giant elk (megaloceros giganteus)*, giant beaver (castoroides ohioensis), wooly mammoth (mammuthus primigenius),
sabre-toothed cat (smilodon fatalis), dire wolf (canis dirus), giant ground sloth (megatherium americanum), mastodon (mastodon americanum)
* - see Errata section
The TL mentions Megaloceros living in the empty North America. Unless these large deer migrated there (despite humans not having migrated to the Americas in the TL's prehistory), Megaloceros shouldn't be there. In OTL, they were a purely Eurasian species of deer. An Old World deer species migrating to the Americas in an ATL, but prehistoric humans not managing the same, rather strains believability. However, this is just a minor error.
Another possible error on Doug Hoff's part is identifying Newfoundland as Markland. Contemporary historians generally surmise that the Markland described by the Scandinavians who visited North America was probably Labrador, with Vinland being Newfoundland. Doug explicitly positions his story's Vinland in OTL New Brunswick and the areas to the north. Of course, given the relative vagueness of the Scandinavians' oral tradition about their visit, it's hard to precisely pinpoint which region was which. Given the alternate timeline, it's possible the generic terms of the Scandinavians could be applied to several areas of North America's coastal northeast.