Earthly is an open-source tool designed to address the challenge of reproducible builds, allowing developers to replicate build processes both locally and in CI environments, thereby eliminating discrepancies caused by environmental differences. The tool utilizes Earthfiles, which combine elements of a Dockerfile and a Makefile, to encapsulate build steps such as compiling, testing, and containerizing projects, as demonstrated through a Scala example. By running builds in a Docker container, Earthly ensures consistent results across different environments, allowing developers to quickly identify and resolve build failures. Additionally, Earthly offers solutions for more advanced build challenges like parallelization, caching, and multi-language builds, with further resources and tutorials available for users seeking to optimize their build processes.