Because all Espresso Logic APIs are REST APIs, they can be used by any REST-compatible tools and languages. For instance, you can use curl, or your web browser.
But these tools are a bit tedious: you have to manually set HTTP headers, and remember the ID of various objects.
Espresso Logic provides two command-line tools to make this easier: espresso-cli and espresso-admin-cli
espresso-cli is a simple command-line tool that allows you to easily invoke an Espresso Logic API. This can be handy if you need to script certain interactions, or if you're just a command-line kind of person.
The Espresso command line is documented on its GitHub page.
espresso-admin-cli is a command-line tool specifically geared towards administering Espresso Logic services and APIs.
Advanced Espresso users will no doubt realize that it is, in fact, entirely possible to administer an Espresso service using espresso-cli -- that is true, but the admin CLI makes it quite a bit easier.
The Espresso Admin command line is documented on its GitHub page.