Act vs Postmark

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.

Postmark is Transactional email API focused on fast, reliable delivery with detailed analytics and template support.. It is available under a freemium model. This tool falls under the developer utilities category.