Act vs Mailgun

act is an open-source command-line tool that runs GitHub Actions workflows locally using Docker containers. It reads workflow files from .github/workflows/ and executes them with environment variables and filesystem configurations matching GitHub's hosted runners. The tool enables fast local feedback on workflow changes without requiring commits and pushes to a remote repository.

Mailgun is email API for sending, receiving, and tracking transactional email with validation and routing features. It provides comprehensive features for development workflows. The tool is actively maintained with regular updates and strong community/vendor support.