Substance Painter, Substance Designer, and Bitmap2Material. There’s a whole package for all three and I think they’re perfect for any artist who needs to texture things.
Link: https://www.allegorithmic.com/
P.S. ZBrush is more for sculpting but it can definitely be used for normal maps, I think you would need to render the normal/height maps so they can be imported into UE4.
Edit: Damnit @ZacD, beat me to it!