* Spice3 is the most famous and used circuit simulator. It was developed University of California at Berkeley (UCB), by "a cast of thousand" (as they say).
* Cider is a mixed-level simulator that already includes Spice3f5 and adds a device simulator to it: DSIM. Cider couples the circuit level simulator to the device simulator to provide greater simulation accuracy (at the expense of greater simulation time). Critical devices can be described with technology parameters (numerical models) and non critical ones with the original spice's compact models.
* Xspice is an extension to Spice3 that provides code modeling support and simulation of digital components through an embedded event driven algorithm.