LTspice - LTspice® is a high performance SPICE simulation software, schematic capture and waveform viewer with enhancements and models for easing the simulation of analog circuits.
Arduino IDE - Arduino is an open-source electronics prototyping platform based on flexible, easy-to-use hardware...
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.
embedXcode - embedXcode is a template for Xcode.
PyLab_Works - PyLab_Works is a free and open source replacement for LabView + MatLab, written in pure Python.
InstaPart - Build circuit boards faster with parts delivered in <24 hrs