Ultima Founding
A Space Marine founding taking place in the early 42nd Millennium (8th Edition), the Ultima Founding is unique as all Ultima Founding chapters are entirely made up of Primaris Marines, the shiny true-scale NuMarines with the latest and greatest technology, which is what happened when Roboute Guilliman told Belisarius Cawl than normal Space Marines weren't cool enough.
While many of the first NuMarines were sent to reinforce existing chapters (with Guilliman's Ultramarines being the first, of course), Guilliman also ordered a host of brand new chapters created out of whole cloth. These chapters are the Ultima Founding.
All of the original First Founding chapters were represented in these new chapters, with each chapter tracing their history like any other successor chapter. Yes, even the Space Wolves, who are undoubtedly thankful for a Successor Chapter which hasn't devolved into mutants. It is unknown if Ultima Founding Successor Chapters will contain the Crunch from their various chapters (for example, Blood Angel Ultima Successor chapters having the black rage); the announcement is intentionally vague. It is possible that you will be able to choose between using special rules like the Death Company and not, or that these special rules will be included in later books.
Ultima Founding chapters were mostly given homeworlds on the edge of the Great Rift to act as a bulwark against Chaos, although some were created to replace destroyed chapters and were given their empty Fortress Monasteries to inhabit.
Games Workshop appears to be intentionally pushing players to create their own chapters this time, going so far as to include a coloring book style "design your own chapter" thing with the announcement of the Ultima Founding.
Ultima Founding Traitor Legion Loyalists?
As mentioned in Dark Imperium, Cawl apparently either planned to or outright did create Ultima Founding chapters out of ALL the original first founding chapters -- including the Traitor Legions, as well as the two infamously Lost Legions, II and XI. It is unknown if they were finished before RG objected to them, or if they were created and subsequently purged. Guilliman personally suspects that Cawl probably had them made despite his objection.