Programmatic G-Code Generators
In addition, Will Winder's Java Universal-G-Code-Sender has gained a number of features for manipulating G-code files.
3 dimensional control of a beetle (replacement turtle) allows programmatic design of 3D objects in: http://beetleblocks.com/
Excellent examples of directly programming G-code: http://www.sawmillcreek.org/showthread.php?244397-Some-CNC-work
Libraries and Languages
|Python front-end for OpenSCAD||SolidyPy||Use a Python IDE and the Python language to treat objects like objects (not text), use existing OpenSCAD modules, manipulate objects and copy shapes. Extensible.|
|Python front-end for OpenSCAD||SolidPython||A python frontend for solid modelling.
https://pypi.org/project/viewscad/ --- Jupyter Notebook interface
|Python front-end for OpenSCAD||openpyscad||Python library to generate OpenSCAD source intuitively.
|Java front-end for OpenSCAD||JavaSCAD||Representation of OpenSCAD primitive objects with Java objects allowing the building of more complex ones from them.|
|Python development framework||PythonOCC||3D CAD/CAE/PLM development framework for the Python programming language --- provides advanced 2d and 3d geometry modeling structures and algorithms: Bézier BSplines Extrude/revolve/sweep.|
|Python halftoning program||pixel machining||Python program to make halftone images out of pixel maps using the Python Imaging Library.|
|G-Code pre-processor written in Python||Mecode||Convenient, human-readable layer just above GCode. Written in Python.|
|G-Code pre-processor||JGCGen||A G-Code preprocessor and generator based on Apache Velocity. http://www.vagrearg.org/content/gcmc|
|G-Code pre-processor||gcmc||Compiler with a context-free grammar and procedural format, which runs scripts to make G-code for a CNC mill. Supports variables and advanced math (scalars, vectors and vector-lists) including mil/mm unit-conversions.|
|G-Code library written in Python||preGrbl||Checks and validates g-code compatibility, converts g-code into a more grbl-friendly format, and provides a way to implement and translate canned cycles and other high-level tasks. Written in Python.|
|TCL g-code preprocessor code||gcode and example.tcl||TCL program which allows one to program in G-code using TCL to implement loops and other control structures.|
|Language and IDE (opensource)||Processing||Processing is an open source programming language and environment to create images, animations, and interactions. See GCtrl and SuperSkein 1.0.|
|Language and IDE (opensource)||NodeBox||Cross-platform, node-based GUI for efficient data visualizations and generative design. Used to make a sundial. Spirograph example sent to a CNC machine and milled.
Note that it uses pixels/points, and scaling and other values are limited in precision, work which requires accuracy would have to be specified in terms of native units.
|PostScript to G-Code Converter||ps2gc source||Command-line utility to convert from (some) PostScript formats to G-Code --- affords the possibility of using tools like Asymptote or METAPOST, may be what was used for NodeBox (above). CF the reverse, gcode2eps which would be very useful for previewing on systems which have Display PostScript.|
|Python and CNC presentation||Python: A "Toy" Language||PyCon presentation on using Python (and IPy Notebook) to generate G-code.|
|Python utilities||gctools||A set of Python scripts to help create and manipulate CNC gcode files.|
|Python library||pyfab||Python library for fab/lab control.See also dxf 1.1.1 a Python library to generate DXFs.|
|Apt interpreter||APTOS||Opensource Apt translator project. Consists of several CAM applications, based on the Apt programming language. See APT Tutorial.|
|G-code utility||padder||Utility to add spaces to G-Code (also includes Scan2 CNC (convert image to G-Code) and Wrapper (wrap a toolpath around a cylinder for those who have a lathe as a 4th Axis).|
|G-code utility||CNC G Code Arcs to Lines Conversion Program||Utility to convert all arcs to straight line segments.|
- http://commonwealthrobotics.com/ --- BowlerStudio --- tutorials available: http://commonwealthrobotics.com/BowlerStudio/Welcome-To-BowlerStudio/ 
3D printing oriented: https://github.com/jminardi/mecode
- Sample project, a 3-in-1 dock for the Surface: https://github.com/Microsoft/3-in-1-dock
http://www.mattkeeter.com/projects/kokopelli/  --- deprecated in favour of http://www.mattkeeter.com/projects/antimony/3/ https://github.com/mkeeter/antimony and https://github.com/libfive/libfive
Python stuff to add for OpenSCAD from the mailing list (find link in forum for footnote)
https://www.codelv.com/projects/declaracad/ --- language and application to build 3D models using a subset of the python language called enaml
https://github.com/avalero/OOML https://hackaday.com/2017/01/03/ditch-openscad-for-c/ https://www.researchgate.net/publication/254034593_Boosting_mechanical_design_with_the_C_OOML_and_open_source_3D_printers
Vector graphic languages
Logo is notable for being the first, and there are many implementations.
METAPOST --- https://commons.m.wikimedia.org/wiki/File:Cribbage_Board.svg --- note that MP can now make SVGs directly (and there is wiki support: https://www.mediawiki.org/wiki/Extension:Metapost ) --- note a technique for loading the JSON from an OpenSCAD customizer and using it to generate a PDF or SVG: http://community.carbide3d.com/t/cnc-finger-joint-box/8880 --- c.f., http://pyx.sourceforge.net/examples/drawing/metapost.html
Arguably SVG itself can be hand-coded (the same can be said of PostScript). There are a number of SVG-specific tools:
- http://projects.haskell.org/diagrams/ --- flexible, declarative domain-specific language for creating vector graphics, using the Haskell programming language.  c.f., http://savannah.nongnu.org/projects/funcmp/
- https://nvbn.github.io/2015/05/28/svg-animation/ --- clojurescript library
- Oblivion Github  --- programming language that compiles to SVG files.... designed to visualize code and create ... illustrations. Features: SVG-specific data structures and operators, Simple, Ruby/Python like syntax, Runs in the browser, or in NodeJS, Recursion and functional programming support, Immutable Python-style lists
- syntax-highlighting mode for NotePad++
- (free) Editor just for G-Code with syntax highlighting: http://www.cnccoder.com/
- EdytorNC --- Text editor for CNC programmers. Features include: bolt holes calculation; solutions of triangles calculation; speed, feed calculation; conversion inch/mm, mm/inch; code coloring; RS232 data transmission
- https://bitbucket.org/Groomblecom/gcode-editor --- Java (Swing) app intended for editing G-code for 3D printers  
- Gedit --- has a G-code syntax highlighting mode.
- https://atom.io/packages/g-code