eclipse

 a multi-language software development environment comprising an integrated development environment (IDE) and an extensible plug-in system. It is written mostly in Java and can be used to develop applications in Java and, by means of various plug-ins, other programming languages including Ada, C, C++, COBOL, Perl, PHP, Python, R, Ruby (including Ruby on Rails framework), Scala, Clojure, Groovy and Scheme. It can also be used to develop packages for the software Mathematica. Development environments include the Eclipse JDT (Java Development Toolkit) for Java, Eclipse CDT for C/C++, and Eclipse PDT for PHP, among others.

qtoctave

QtOctave is a graphical user interface for gnu octave, which is an open source program alternative to Matlab.

xcircuit

XCircuit is a UNIX/X11 (and Windows, if you have an X-Server running, or Windows API, if not) program for drawing publishable-quality electrical circuit schematic diagrams and related figures, and produce circuit netlists through schematic capture.
XCircuit regards circuits as inherently hierarchical, and writes both hierarchical PostScript output and hierarchical SPICE netlists. Circuit components are savedin and retrieved from libraries which are fully editable. XCircuit does not separate artistic expression from circuit drawing; itmaintains flexiblity in style without compromising the power of schematic capture.

QEMU

QEMU is a generic and open source machine emulator and virtualizer.

Dia

Dia is inspired by the commercial Windows program 'Visio', though more geared towards informal diagrams for casual use. It can be usedto draw many different kinds of diagrams. It currently has special objects to help draw entity relationship diagrams, UML diagrams, flowcharts, network diagrams, and many other diagrams. It is also possible to add support for new shapes by writing simple XML files, using a subset of SVG to draw the shape.

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