Retroplayer:
It may not seem obvious to someone first starting out, but there is "Arduino, the hardware", and "Arduino, the software." And they are really separate from each other.
I would go a step further - there's really:
Arduino, the hardware.
Arduino, the runtime software.
Arduino, the integrated development environment.
The hardware and runtime software is great.
The IDE isn't great but it's free, and makes it easy to get started in firmware development.