Ghostnote - Add notes to anything.
KiCad - A Cross Platform and Open Source Electronics Design Automation Suite
Somnote - More often than not, note-taking is a pressing, off the cuff movement that requests a quick and productive approach.
Proteus PCB design - Proteus PCB design combines the schematic capture and ARES PCB layout programs to provide a...
Box Notes - Box Notes: take meeting notes, share status updates and plan projects together instantly. Online, across devices.
QUCS - Qucs, briefly for Quite Universal Circuit Simulator, is an integrated circuit simulator which means you are able to setup a circuit with a graphical user interface (GUI) and simulate the large-signal, small-signal and noise behaviour of the circuit.