These are the open source management related tooling that I am tracking on as part of my research, and can be used as part of the API command line interface process.
CLI interface to Algorithmia algorithms and data API
The Apiary CLI gem is a command line tool for developing and previewing API Blueprint documents locally. It can also be used for pushing updated documents to and fetching existing documents from Apiary.io.
A Command Line Interface (CLI) for apiman
DCOS CLI for ArangoDB
Command-line client for Tutum
A small package for building command line apps in Go
A Diffbot API client for Powershell
CLI for Docker Cloud
A command line tool for DigitalOcean services
command line interface to access Dropbox API
Facebook Command Line Interface
The Firebase Command Line Tools
Google Calendar Command Line Interface
A command-line interface to the GitHub Issues API v2.
A command-line interface and Python API wrapper for Google Analytics.
Command line tool for the Iron.io platform.
Command line interface to Mapbox Web Services
Medium for Hackers - :computer: A CLI for Medium Stories.
Newman is a command-line collection runner for Postman
Docker images for Newman Collection Runner
A collection of tools to help with PHP command line utilities
PowerShell Module to interact with AYLIEN Text Analysis API - a package consisting of eight differen
A CLI for Rackspace
CLI for Reindex
Unlocking the potential of the WP REST API at the command line
Scrapinghub Command Line Client
Generates a command-line interface for any Swagger Specification
Thor is a toolkit for building powerful command-line interfaces.
Command line interface and Ruby client for the Tumblr API (v2)
Webhook Command Line Interface.
A command line interface for WordPress
Command-line interface for WordPress using REST API written in Go
The Zonemaster CLI - part of the Zonemaster project
If there is an "open source tool" that should be listed here, submit as a Github Issue, and I will consider adding.