Python developers rejoice!
Pipenv is a dependency manager for Python projects.
It works similarly to other popular dependency managers, like npm for NodeJS, or bundler for Ruby.
Pipenv combines and streamlines the use of pip and virtualenv.

Getting started

Pipenv can be installed via pip:
pip install --user pipenv

If on macOS, I'd recommend installing Pipenv via brew:
brew install pipenv

Initialize a pipenv environment for any Python project

Initialize a Pipenv environment with Python 2.x:
pipenv --two

Initialize a Pipenv environment with Python 3.x:
pipenv --three

Notice that a new file will be created named Pipfile.
This file is similar to a Gemfile or package.json on Ruby and NodeJS respectively. Pipfile lists all top level dependencies grouped into packages and dev-packages.

Installing Python dependencies

Let's suppose that the popular library requests is a requirement.

Install the latest requests version:
pipenv install requests

or install a specific requests version:
pipenv install requests==2.18.4

or install a package for dev purposes:
pipenv install nosetests --dev

In all cases the Pipfile will get updated, with either a * version, or the specific requested version.
In addition to the Pipfile, a new file named Pipfile.lock will be created.
This file is similar to Gemfile.lock or package-lock.json on Ruby and NodeJS respectively.
Pipfile.lock lists all top level dependencies as well as any sub-dependencies.

It's very important to commit and keep both Pipfile and Pipfile.lock files under version control, as these will be used to re-create the virtualenv by fellow contributors or via a deployment script etc.

Displaying Python dependencies

Apart from inspecting Pipfile and Pipfile.lock files, there is a handy Pipenv feature:
pipenv graph

Running Python commands

The only downside of Pipenv, is that all Python commands need to be prefixed by pipenv run, for example:
pipenv run python --version

or
pipenv run python app.py

Virtualenv shell shortcut

Pipenv has a nice little feature that spawns a bash shell within the virtualenv:
pipenv shell

Running python on the spawned bash shell, will start a Python shell within the virtualenv.
If for example requests package was installed, import requests will just work.

Uninstalling Python dependencies

Uninstall a specific package:
pipenv uninstall requests

or uninstall all packages:
pipenv uninstall --all

Remove a Pipenv virtualenv

Clean up a virtualenv:
pipenv --rm

Re-create a Pipenv virtualenv from Pipfile/Pipfile.lock

Create a Pipenv virtualenv and install all dependencies is as simple as:
pipenv install

Is pyenv still relevant?

Pipenv is just a dependency manager, pyenv is still relevant for managing different Python versions.
Moreover Pipenv supports installing Python versions with pyenv when needed.

Conclusion

Pipenv is a great tool, something that was really missing from the Python ecosystem. I am already using it in production, and I highly recommend it.