Buck2 vs FASTBuild

Buck2 is a free build system from Meta for large-scale repositories that combine multiple programming languages. It uses Starlark rules, a dynamic dependency graph, and incremental actions to support extensible builds. Its language table lists prelude rules for C/C++, Erlang, Go, Haskell, Java, Kotlin, OCaml, Python, and Rust, though usability varies by language. Build actions can run remotely through services exposing Bazel's remote execution API; the project lists BuildBarn, BuildBuddy, EngFlow, and NativeLink as compatible with its distributed compilation support. Buck2 supports filesystem watching and can integrate with Meta's optional Eden virtual filesystem. Rules are hermetic by default and missing dependencies are errors, but local-only build steps are not sandboxed. The project describes Buck2 as early-stage and says it has no stable release tag; its latest binary tag changes with repository pushes. It warns that outside users may encounter rough edges, missing features, and missing toolchains. Source and binaries are available under MIT and Apache-2.0 licenses. The project directs users to GitHub for issue reports and offers a community Discord server.

FASTBuild is an open-source build system for compiling software across Linux, macOS and Windows. It runs compilation work across worker threads, can reuse results from local or network caches, and can distribute builds among networked machines when their settings and worker setup are compatible. The maker says caching can accelerate compile times up to 10x. Some compiler settings do not support caching or distribution; FASTBuild handles affected objects without caching or builds them locally. Supported toolchains include MSVC, GCC, SNC, Clang, GreenHills, CodeWarrior and NVCC, plus syntactically compatible command-line compilers. It can combine C++ files into Unity or Blob builds, while allowing writable files to be built individually for quicker iteration. FASTBuild can generate Visual Studio and XCode project files. The maker describes it as a self-contained executable that needs no installation or dependencies beyond compiler tools. It is free, with commercial use and redistribution allowed under license conditions; the license provides the software without warranty. The listed current release is v1.20, released 26-Apr-2026.