Opentofu is Terraform 🤣 I generally don't throw that out there to prevent confusing people, but I prefer it, honestly.

Packer builds images you can upload to cloud platforms.

Terraform/Opentofu executes API calls to orchestrate spinning things up and down.

Cloudinit is the native built-in bootstrap framework of instances themselves that all the major cloud providers support. It's what executes as "userdata" as some call it. Check your cloud provider docs for how to hook it in.