LTspice

LTspice is free graphic design software that enables you to easily create circuit designs. Developed by Analog Devices, this multimedia program is a high-performing SPICE-based analog electronic circuit simulator that can draft, probe, and analyze the performance of your circuit designs before you craft their prototype and test them in the field. It provides various convenient features that both beginner and advanced users will appreciate and has enough online documentation for reference.

Features
One of this programs best aspects is that it is freeware but is not artificially restricted to limit its capabilities. Its also great as an educational tool due to its extensive documentation so beginner users can easily take a stab at it. However, its interface is highly uninspiring due to its outdated appearance. The layout of features is straightforward enough but its not as sleek-looking as you would hope for a circuit simulator.

Library
It also comes with an extensive library of macro models and passive components, covering most of the developers other power management and signal chain software. It can provide schematic captures and even lets you configure each component individually.

Still a versatile tool
All in all, LTspice is a powerful piece of software for any type of user requiring electronic circuit simulations. While its user interface can be pretty bland, its features perform much better compared to SPICE. Plus, being available at no cost more than makes up for its shortcomings since its a more desirable program compared to its rivals. If youre looking for a free circuit design tool, then this one is a highly recommended choice.