Online tool to draw wiring and circuit diagrams, with a built-in SPICE simulator so you can test a circuit before you build it.

KiCad is described as 'Open source software suite for electronic design automation (EDA) - designing schematics of electronic circuits and printed circuit boards (PCB). KiCad is developed by Jean-Pierre Charras. And features an integrated environment between schematic capture, bill of' and is a very popular circuit simulator in the education & reference category. There are more than 50 alternatives to KiCad for a variety of platforms, including Windows, Mac, Linux, Web-based and Flathub apps. The best KiCad alternative is Fritzing. It's not free, so if you're looking for a free alternative, you could try Velxio or LibrePCB. Other great apps like KiCad are Autodesk EAGLE, Square Sketch, Altium Designer and Proteus PCB design.
Online tool to draw wiring and circuit diagrams, with a built-in SPICE simulator so you can test a circuit before you build it.
