I've been on an internet wide search for free software for all kinds of different applications and it's amazing what's available even to the point where a person may not have to spent one cent on software for the rest of their life. One of those categories is analog circuit simulation. I figured perhaps others can benefit from what I've found. If you want to better learn electronics or play around with different circuits or wire up virtual synth modules to see how they work without having to buy actual components, power supply and breadboard, then here's some of the best ones I've found.
Texas Instrument's Tina-TI analog circuit sim for Windows. This is the easiest one to use and I'm able to do things without looking at a manual.
http://www.ti.com/tool/tina-tiLinear Technology's LTSpice IV analog (and a little bit of digital) circuit sim for Windows. Will probably need some time to learn how to get plots and graphs out of it, and all the opamps are Linear Technology versions, so it's a bit biased in that respect.
http://www.linear.com/designtools/software/#LTspiceQUCS open source mixed mode analog/digital circuit sim for Windows, Mac, Linux. I couldn't get the Mac version to load but the Windows version loaded up okay though I'm confused about whether I need to install the FreeHDL to run simulations or not. Looks like a really nice one, but looks like a steep learning curve if you need to define your own Opamp types. Be sure to download the workbook.pdf to learn how to use the program.
http://qucs.sourceforge.net/docs.htmlEven though this is mostly about analog, just incase you only need digital circuit simulation, then it doesn't get easier and more fun than Ligisim for Windows or Mac (Needs Java installed). It's small, solid and stable and I used it to design a parallel divider that can divide two 4 bit numbers without clocking bits through one at a time like a CPU does (see link at bottom for picture). It even allows entering truth tables and from those it can automatically generate boolean equations, perform Karnough map reduction, and generate circuitry for you.
http://ozark.hendrix.edu/~burch/logisim/download.htmlhttp://i127.photobucket.com/albums/p122/Elhardt/Ken%20Elhardt/Divider4x4.jpgHave fun building or designing circuits,
-Elhardt