I have just found some useful software online. Basically like Visio but totally free and open source.
It can be used online in a browser or downloaded as a stand-alone application for Linux, Mac and even Windows.

Comes with a load of electronic symbols and other shapes. Has connectors that stay linked when you move shapes.

Have a look at https://www.draw.io/

Perhaps you have already found this but it's new to me!
I have been playing. Here is my first effort: (for the actual draw.io file, change the txt extension to xml before opening)

 

Hello,

Then you probably also know DIA:
http://dia-installer.de/
You can add a list of shapes to the program:
http://dia-installer.de/shapes/index.html

Bertus

 

I have had a play with DIA - quite a while ago. Found it wanting. But it might have improved since then.

I have Visio here. Very good for all types of diagrams and especially flowcharts. I have been using it since the mid 90's when it was by Shapeware. After it was taken over by Microsoft, the application has been well dumbed-down but all the original functionality is still there if you dig deep.

Mulit-platform software is the way forward these days. I use Linux just as much (possibly more than) Windows and I hate the hassles of licensing or subscriptions.

 

There is also free CircuitLab.
Max.

 

I have put Paint CAD into the public Domain.

Introduction and PaintCAD