Real-time simulation

Hello all.
   I was wondering if anyone had given any thought to a realtime analog 
simulation tool? In the past I had been involved in testing some 
"electronics workbench". It was geared towards helping students plays 
with circuits w/o really playing with circuits. In addition to that I 
spent a lot of time using a free package called Analog (written by John 
Lazarro) which was designed to simulate analog circuitry in subthreshold 
behavior. (This is Carver Meade stuff if that means anything to anyone.)
  Anyways, I have been kicking around the idea of designing an improved 
"workbench" based on GNUcap for both educational and design purposes. 
Anybody?

-JD