Microcap 12 is a formerly commercial circuit simulator that has been made freeware, it was developed by Spectrum Software since 1982 with the final release coming in 2020, while there will no longer be any updates Microcap 12 is fully functional and mature software.
Microcap has a lot of functionality so as might be expected the interface is a tad cluttered, however compared with some other professional circuit simulation software it really isn’t too bad, the manual, user guide and reference manual provides plenty of help.
There is a great deal of customization options available including interface layout, keyboard shortcuts, colours and fonts which makes it very versatile.
The included parts library is very extensive containing over 45,000 parts, including useful macro models, while it may be a bit lacking in terms of the most modern parts, there is still enough for essentially every need, in addition in can import standard SPICE models and subcircuits.
A wide variety of simulations are available, from the standard DC, AC and transient to harmonic / intermodulation distortion, stability and optimization, for a free simulator this is by far the best I’ve seen, a number of interactive options are included as well such as sliders and animated parts which makes it very good for educational usage.
There is an extensive amount of graphing options including formulae, annotation, FFT, monte carlo and more making it a very powerful tool.
Microcap 12 is currently the best value circuit simulator that can be had, it even beats a number of commercial products in terms of functionality and component library, what I find more surprising is that Spectrum Software have decided to make this freely available rather than simply vanish like so many companies do these days.
You can get Microcap 12 for free from the Spectrum Software website.