(I'm hoping Mitchell is going to have an answer to that)
Or OpenTF if you want to same thing minus the licensing mess
I tried to understand what is it, how it works, what is it good for, but ... never managed to. It still has the same "build control planes without needing to write code" on its website. okay, it says "orchestrate applications and infrastructure". that's at least makes sense when the context is Terraform and Pulumi.
okay, in the quickstart the whole thing seems like code. but okay.
ah, so you can use k8s CRDs to define cloud stuff (like S3 buckets and GCP GCS buckets and whatnot), not bad, but super verbose.
Crossplane -> Same end result as Terraform but you use K8s resources in YAML to describe your infra.
I hope that helps. But I agree that the crossplane/upbound marketing is super confusing.
Yes, technically you can do that with Terraform but in my experience it doesn't work great for code deploys (which tend to have procedural steps)
It's a bit like Elasticsearch, I think—it's gotten big enough it won't be a quick death, but I don't see Hashi's products growing/dominating as much now as I did a couple years ago.
(As an aside, I'd like to thank Mitchell for his work over the years, Vagrant especially was huge in my infrastructure work, and Terraform was a great companion to Ansible and CloudFormation as we automated more and more stuff.)