pkgx is a cross-platform package runner and package manager from the creator of Homebrew, Max Howell. Instead of installing tools globally, pkgx node@20 fetches an isolated build of Node 20 into ~/.pkgx and runs it, resolving its transitive dependencies on the fly from a distributed registry of pre-built binaries.
Packages are defined declaratively in the pantry repository (github.com/pkgxdev/pantry) as YAML specs that describe how to build each project from source for macOS (arm64/x86_64) and Linux (arm64/x86_64). The builds are content-addressed and relocatable, which means multiple versions coexist without conflict and activation is just a matter of prepending the right directories to PATH. A dev shim hooks into your shell so that entering a project directory with a package.json, pyproject.toml, or similar manifest automatically makes the correct versions of node, python, or go available in that shell, similar to direnv combined with asdf or mise.
pkgx is MIT-licensed and competes with Homebrew, asdf, mise, Nix, and devbox. Its niche is being daemonless, not requiring sudo, and being usable as a one-off runner in CI (pkgx +node@20 npm test) without committing to a package manager installation on the runner.