Snap Circuits ® | Electronic and
Provides electronic components that snap together without need of soldering.
SPICE - Wikipedia
This is a general discussion of the spice circuit simulation language, with links to various resources.
Ngspice circuit simulator - NEWS
The documentation for the Ngspice variant of spice is available here. The program is available for various platforms, including Linux.
SPICE-Based Analog Simulation Program - TINA-TI - TI Software
This is a spice variant for Windows. It requires registration and has some restrictions on its use.