Another reason the 5620 was botched so badly was that AT&T wanted >=
$2000 for the development kit (read: C compiler and libraries) for it.
Not a good way to get lots of 3rd party application developers
on your bandwagon.
I used one for a year or so; it was the first windowing system I'd
used and the only one I've really liked. For about 10 years I've been
using 9wm, which gives a similar feel (at least to me). Those who want
to go all the way should adopt 9term as well. (I generally run xterm +
bash these days, although for a long while it was 9term + es/rc.)
Somewhere, I have an X version of the 5620 font. I found that it
wasn't so pretty. I've been using the pelm-latin1-9 font from the sam
distribution for years.
Norman forgot to mention that the most long-lived split-design application
is Rob Pike's sam editor, still available for X11 and still in use on
Plan 9.
Arnold