CUE offers a very fluent syntax for composing configuration data, it also has many great features enabling extensive validation of configuration data as part template definition.
Using CUE can be a little challenging at first, especially because it's entirely up to the user how they want to consume the results and whether any data would be written to files.
kue provides as simple tool for generating configuration with CUE template by introducting a few simple conventions.
The aim is to focus primarily on Kubernetes and GitOps use-cases, but it is just an experiment right now.