General

What is PlatformIO?

Please refer to What is PlatformIO?

What is .pio directory

Please refer to workspace_dir.

Command completion in Terminal

Please refer to PlatformIO Shell Completion.

99-platformio-udev.rules

Please refer to 99-platformio-udev.rules.

Multiple PlatformIO Cores in a system

Please refer to Multiple PlatformIO Cores in a system.