XCos SPICE block
SPICE is an electronic circuit simulator. The goal of this project is to add a SPICE block into XCos. With such a block, you should be able to load a circuit as a SPICE file and then provide input voltage / current as inputs of the block and get simulated voltage / current as block ouputs.
The key idea of the enhancement is to use ngspice (or any other opensource software) as the simulation engine for SPICE described parts while keeping the Scicos simulation engine for the remaining blocks.
An integration of another external simulation engine (Modelicac) has already been performed on Xcos/Scicos. You can read some documentation papers there.
There is an open source SPICE simulator: NGSpice.
Some information related to SPICE are available on wikipedia.
You can get history information related to SPICE here.
A brief overview of the SPICE language : http://www.seas.upenn.edu/~jan/spice/spice.overview.html