Most developers use BuildKit daily without realizing it. When you run `docker build`, BuildKit is the engine behind it, but reducing it to "the thing that builds Dockerfiles" misses the point entirely. BuildKit is a general-purpose, pluggable build framework that can produce OCI images, tarballs, local directories, APK packages, RPMs, or anything describable as a directed acyclic graph of filesystem operations.

At BuildKit's core is LLB (Low-Level Build definition), a binary protocol that describes a DAG of filesystem operations. This content-addressable system means identical operations produce identical hashes, enabling aggressive caching. The Dockerfile is just one frontend; BuildKit can accept any build definition that produces valid LLB. You can write frontends that read YAML, JSON, TOML, or custom DSLs, and BuildKit executes them the same way it executes Dockerfiles.

BuildKit's `--output` flag unlocks practical non-image use cases. You can export results as `type=local,dest=./out` to dump final filesystems to local directories, or `type=tar` for tarballs. Projects like Earthly, Dagger, and Depot all use BuildKit's LLB as their execution engine. The framework handles caching, parallelism, and reproducibility for free, making it valuable for any tool that needs to compile code, produce artifacts, or orchestrate multi-step builds.