QElectroTech is an open source tool for drawing these types of diagrams. It consists of two tools: an element editor for creating schematic symbols and a diagram editor for creating your drawings.

[It includes] drag-and-drop, copy-and-paste, in-place text editing ... mxgraph is another open source, pure JavaScript, client-side library for creating interactive diagrams that renders to ...

a fully open source solution for building web-based diagram editors. Eclipse GLSP is an extensible platform to develop diagramming solutions of all kinds. GLSP can be used in Eclipse Theia ...