Atmel gave out the IDE for free, then someone noticed and came out with the Arduino. Bam! Instant market penetration.
Actually Wiring (http://wiring.org.co/) was first, then Arduino took the code to use it on cheaper chips. And Arduino keeps using code from Wiring, even today, without a proper attribution. It's true they stick to Wiring's license, but it would be nice if they let the world know it wasn't their idea.
"Today's robots are very primitive, capable of understanding only a few simple instructions such as 'go left', 'go right', and 'build car'." --John Sladek