Mantle Core 0.1.0

Mantle Core 0.1.0 for Unreal Engine 5.8 (Win64).

Fab: in the Fab publishing portal, add a Project Version for UE 5.8 and paste the link to MantleCore-0.1.0-UE5.8.zip below. Fab downloads it without signing in, so this works only while the repo is public.