"Reverse"/creating from existing cloud resources

Terraformer : https://github.com/GoogleCloudPlatform/terraformer

Aztfy (Azure only) : https://github.com/Azure/aztfy

FinOps / Cost :

Infracost (estimation) : https://github.com/infracost/infracost

Terratag (tagging) : https://github.com/env0/terratag

Terraform frameworks

Terragrunt : https://github.com/gruntwork-io/terragrunt

Terraspace : https://terraspace.cloud/

Policy as code :

OPA : https://github.com/open-policy-agent/opa

Static code analysis

checkov : https://github.com/bridgecrewio/checkov

tfsec : https://github.com/aquasecurity/tfsec

terrascan : https://github.com/tenable/terrascan

kics : https://github.com/Checkmarx/kics

Autres outils Terraform

https://github.com/shuaibiyy/awesome-terraform

https://github.com/runatlantis/atlantis