It's not another JDK, its Amazon build of the OpenJDK, like Azul has been doing for a few years.

Yes, perhaps better thought of as a distribution or packaging. Somewhat analogous to linux distributions.

I thought Azul was a bit more customised around the gc, so not quite the same JVM?

I think you are talking about their other offers? I was referring to ones at the bottom of this page under section: "Download Azul Zulu Builds of OpenJDK"

https://www.azul.com/downloads/?package=jdk

An alternative to the standard JDK that's supported by Oracle. Generally, the less stuff Oracle controls, the better (not to say Amazon having control is inherently better, but imo, it's better than Oracle)

Most of Amazon's work is served on a plate by Oracle, given the ratio of OpenJDK code.

Apparently Oracle changes the license of their openjdk builds a while ago, so big corps decided it'll be safer to maintain their own jdk build in case Oracle's lawyers come knocking.

It's a decent compliant stopgap as IT operations continues its general battle to remove all Oracle products from the environment