This page describes some freely-available SPICE and SPICE-like analog circuit simulators.

Software

•  LTSPICE from Linear Technology. Works under Wine, highly recommended!
  • LtSpiceNotes -- some notes on how to incorporate user models, etc
•  ngspice SPICE Linux?
•  TINA - evaluation version from T.I. windows?

Documentation

• Spice3  User Guide
• One of many  Spice Tutorial

on the web