PlatformIO Core (CLI tool) is a heart of whole PlatformIO ecosystem and consists of
Multi-platform Build System
Development platform and package managers
Integration components (Cloud & Desktop IDE and Continuous Integration).
PlatformIO Core is written in Python 2.7 and works on Windows, macOS, Linux, FreeBSD and ARM-based credit-card sized computers (Raspberry Pi, BeagleBone, CubieBoard, Samsung ARTIK, etc.).
PlatformIO Core provides a rich and documented Command Line Interface (CLI). The other PlatformIO-based software and IDEs are based on PlatformIO Core CLI, such as PlatformIO IDE. In other words, they wrap PlatformIO Core with own GUI.
Note
Please note that you do not need to install PlatformIO Core if you are going to use PlatformIO IDE. PlatformIO Core is built into PlatformIO IDE and you will be able to use it within PlatformIO IDE Terminal.
If you need PlatformIO Core outside PlatformIO IDE, please Install PlatformIO Core Shell Commands.