The Net Yaroze (which means, Let’s do it in Japanese) is was an official hobbyist programmable Playstation from Sony (SCEE).
It was launch in 1997, and I remember reading about it in a Playstation magazine, it was $750 US about $1400 AUD.
At that time I just started programming part-time, and I wasn’t sure I could do it.
In 1998 I started a Diploma in programming and in March 1999, I had a Net Yaroze! (I still have my acceptance letter in my CV!)
Official documentation here:
Well documented here also: