That said, I'd say the key difference is that EnvKey places much more emphasis on security and privacy. Doppler is cloud-hosted and doesn't use end-to-end encryption, so it requires that you trust them to keep your data safe and not make any mistakes in their data security, network security, who they hire, what sub-processors they trust, etc. In my (very biased) opinion, that is not sufficient protection for the most sensitive data.

Doppler also uses a web interface, which is great for convenience and UX, but leaves you vulnerable to compromised browser plugins, XSS, etc. I don't believe browsers are sufficiently secure currently for secrets management (if this changes, we'll add a web interface to EnvKey ASAP!).

There are real costs in terms of UX to end-to-end encryption. EnvKey tries to be as user-friendly as possible, but doesn't compromise on security or privacy. Doppler's design, as I understand it, leans more toward the other side of this tradeoff.

On Terraform--yes, it's easy to use EnvKey with Terraform. The general pattern for integrating EnvKey with any tool or platform is to set your ENVKEYs as secrets in whatever way the platform handles them, then expose each ENVKEY as an environment variable to your VMs, containers, or whatever else you're running. We'll write up a Terraform-specific guide soon to make it as easy as possible.