rapid prototyping for physical computing projects is exploding.
The trend is now clear...
there are a couple of "competitors" but for what I've seen so far Arduino is the best ;-)
compared to the others, Arduino is the best mix between:
low level allowing flexibility,
open source encouraging the masses
and simple enough to reach the designer "oh-my-god-I'm-afraid-of-scripts?" community
;-)
1- d.tools
http://hci.stanford.edu/research/dtools/a stanford project
2- sketch tools
http://www.sketchtools.comhas an excellent resource page..and by the way...massimo, you are famous

you are listed as n° 2 in the resources>artist & designers list
let's make this post a collection of this kind of similar project...
we might all learn from other projects and manage maybe to merge or collaborate...
at the end we are all aiming (more or less) at the same thing.
b.
ps. I intentionally omitted wiring
http://wiring.org.cojust because for me Arduino is Wiring 2.0 ;-)
pps. an excellent discussion about this trend is:
"Sketching in Hardware" by Mike Kuniavsky -- presented at the recent
O'Reilly's Emerging Technology Conference
http://www.orangecone.com/archives/2006/03/etech_06_part_1_1.html