1. Pre-production
It interests me in how many combinations of pre-prod environments exist, as I (naively) expected this to be standardized, but it's not (e.g. https://en.wikipedia.org/wiki/Deployment_environment#Environ... ). I can see the need for two vs four environments for handling different stages of the life-cycle depending on business needs (and budget). Addressing how to choose the right set of environments for a given company/product would be useful.
I also want to say that your product is phenomenal and it has improved the quality of our shop's build and deploy pipeline by an order of magnitude. Thank you.