Since no one answered you, HIP is a compile time target, you use hipify to transform your cuda code, then you compile it with hipcc, and hopefully everything works; or you target HIP directly.

ZLUDA was a translation layer, ala wine for cuda applications.

HIP is something you can put in production and Zluda is a proof-of-concept?

There's no relation per se (apart from AMD once being involved, before asking the developer to take the project offline).

It is worth noting however that they accomplish their goals very differently. ZLUDA is now DoA-ware because of nvidia's use constraint in their license regarding translation layers. HIP doesn't have this issue.

Lol that's like asking what's the difference between the empire state building and the shed in my backyard: one is the runtime that the company that owns/makes the GPUs has been building for 10 years and the other is a (good) solo project.