Bundler was de-facto Ruby’s dependency manager for several years, but became part of the standard library only at version 2.6. Before that, it should’ve been installed separately.
Bundler provides a consistent environment for Ruby projects by tracking and installing the exact gems and versions that are needed.
Since Ruby 2.6, Bundler is a part of Ruby’s standard library.
Bunder is used by creating gemfiles listing all the project dependencies and (optionally) their versions and then using
or Bundler.setup to setup environment where only specified gems and their specified versions could be used.
See Bundler website for extensive documentation on gemfiles creation and Bundler usage.
As a standard library inside project, Bundler could be used for introspection of loaded and required modules.