Tools that help you manage packages as dependencies and might also provide a global package registry
They work based on manifest files that keep track application metadata and needed dependencies, lock files to offer deterministic installs.
pnpm uses hard links and symlinks to save one version of a module only ever once on a disk. When using npm or Yarn for example, if you have 100 projects using the same version of lodash, you will have 100 copies of lodash on disk. With pnpm, lodash will be saved in a single place on the disk and a hard link will put it into the node_modules where it should be installed.