[tomjakubowski]

There is an important distinction to make between package managers and project managers.

In Ruby, for example, Bundler is what I would call a project manager. It installs packages to a place only it knows (or it should know) about, and Bundler or tools that integrate with Bundler wrangle the Gem loader path to control what modules are available to load.

This way the dependencies of any number of project live in complete isolation from one another, including several different versions of the same dependency which is often impossible to achieve using a system package manager like apt or pacman. The end result is similar to something like virtualenv, but with (in my opinion) a friendlier user experience.

These project managers also often include project scaffolding tools and subcommands to run tests, generate documentation, etc. Examples in other languages include Leiningen or Boot for Clojure, Maven for Java, and Cargo[1] for Rust. When used properly and when the creators of a project manager understand its role, they can work in concert with a system-level package manager. Cargo, for example, interoperates beautifully with system packages with great support for linking with system libraries[2].

[1]: http://crates.io/

[2]: http://doc.crates.io/build-script.html#case-study:-linking-t...