BuildKit vs runhcs

BuildKit is a free toolkit for turning source code into build artifacts. It consists of the buildkitd daemon and buildctl client, and uses LLB, a binary format for describing process dependency graphs. Builds can use Dockerfiles or other LLB-compatible frontends, resolve dependencies concurrently, cache instructions, import and export caches, run nested jobs, and collect unused data automatically. BuildKit supports execution without root privileges and OCI (runc) or containerd workers. Results can be exported as images, local directories, tarballs, Docker tarballs, or OCI tarballs. Cache options include inline, registry, local-directory, and GitHub Actions backends; the README marks GitHub Actions, S3, and Azure Blob options experimental. The daemon provides a gRPC API over a Unix socket by default, with TCP sockets also supported. Binaries are available for Linux, macOS, and Windows. The unofficial Homebrew formula for macOS omits buildkitd; the project gives Lima in a Linux virtual machine as one way to run it. BuildKit is licensed under Apache-2.0.

runhcs has no write-up on Specifiction yet; its figures are above.