The Nylas CLI is a versatile tool that allows users to interact with Nylas APIs without the need for an SDK or cURL, streamlining processes for managing emails, calendars, and contacts. Installation is straightforward, particularly on Mac or Linux using Homebrew, and Windows users can utilize WSL or binary installers. Once installed, users can initialize the CLI with their client credentials and perform various operations such as fetching emails, sending messages, creating calendar events, and managing contacts through JSON files. The CLI simplifies interaction with the Nylas platform by storing access tokens and facilitating updates or modifications without re-initialization, offering a powerful alternative to traditional email clients and calendar applications.