OpenTofu is an open-source Infrastructure as Code (IaC) tool for safely and efficiently creating, changing, and versioning infrastructure. It operates as a CLI-driven application where users define infrastructure in declarative HCL configurations, which are parsed into a dependency graph to plan and apply changes across cloud providers. The architecture features modular separation of concerns: configuration loading (internal/configs), state management (internal/backend/internal/states), graph-based planning (internal/plans/internal/dag), encryption (internal/encryption), and a plugin system for providers/provisioners (internal/plugin/internal/getproviders). Key external dependencies include Go cloud SDKs (AWS, Azure, GCP), HCL for parsing, and cty for type system. The tool emphasizes extensibility through interface-based designs: encryption methods and key providers can be plugged in via internal/encryption, backends via internal/backend, and plugins via internal/plugin. State locking, workspace management, and Terraform Cloud integration are built-in features. Development is active with regular releases, comprehensive testing (unit/end-to-end), and maintenance of compatibility with Terraform ecosystem while introducing independent features like native OCI support and enhanced encryption options.