Here is a list of assets that are already available publicly, the license used, and notes about their relevance to the ASWF Asset Repository working group.
Amazon
(via ORCA)
NVIDIA
SpeedTree
Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported (CC BY-NC-SA 3.0)
Epic Games
Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International (CC BY-NC-SA 4.0)
Mike "BEEPLE" Winkelmann
Creative Commons Attribution 4.0 International (CC BY 4.0)
USD ASSET END USER LICENSE AGREEMENT
(Click a download link to see the license text)
Link to full license?
"Licensed for use only with UE4 based products."