[ColinWright]

Several:

* It was bordering on trivial to write programs with a decent GUI;

* The light-weight, integral message passing system was a joy to use;

* It was clean to use;

* It was small and fast to start up.

It's hard to put it into words, it was simply fun to use, and I could enjoy writing real software.

[vram22]

Thanks. I will see if I can try it out at some time, if it works on regular PCs, or I may have to get a Pi. The point about easy GUI development interests me, as well as the speed and the message passing system. I had tried out QNX some time ago, when Photon was the GUI system for it, from a CD that came with a computer magazine. It was small too. It was also a message passing system, IIRC, and was also very fast, I remember noticing that, though I only tried it for a short while.