Netbeans - NetBeans IDE 7.0. Develop desktop, mobile and web applications with Java, PHP, C/C++ and more. Runs on Windows, Linux, Mac OS X and Solaris. NetBeans IDE is open-source and free.
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.
Eclipse - Eclipse is an open source community, whose projects are focused on building an open development platform comprised of extensible frameworks, tools and runtimes for building, deploying and managing software across the lifecycle.
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.
IntelliJ IDEA - Capable and Ergonomic IDE for JVM
PyLab_Works - PyLab_Works is a free and open source replacement for LabView + MatLab, written in pure Python.