I would make a config-management tool similar to Ansible, SaltStack, Chef, etc.
Would be 100% open source, no “enterprise” plan.
Tasks would NOT be declared using an under-powered syntax like YAML or a crappy DSL but rather be pure-elixir.
It would have a built-in web-based GUI and a robust CLI.
It would allow you to describe your environments and services and would realize those declarations in a declarative-infrastructure way.
It would have an opinionated way to store your secrets and configurations.
It would also do the work of Terraform and allow you to “plan” your executions and tell you what will change.
Would have both a masterless and worker based option.
It would allow you to mark environments as “safe” or “production” and keep you from doing bad things to those nodes.
It could also do the work of Jenkins and have excellent github / SCM integrations.