I, Erik de Bruijn, have written a simple interactive controller in PHP (Linux only, sorry!). It behaves like a command line interface, but for your machine.
It will run your G-Code line by line and allow you to make decisions. It will run with interruptions (hence 'interactive controller'), so it is mostly meant for milling/engraving, not for extruding (which is time-critical).
After you've decided (e.g. on cardboard) that the path your tool travels is right, you can run the entire piece at once.
It is meant to have more control over your machine while working with G-Code. You can decide which line of G-Code to run and which to skip (by pressing r(un), [enter] or n(ext), [enter], respectively). You can type your own G-Codes in between. There are aliasses that you can use so you don't have to remember G or M codes.
This is version 0.1, so forgive any mistakes or lack of functionality. It will only run under Linux and needs PHP5 (Debian/Ubuntu: apt-get install php5-cli).
Future versions include a 'WRITE/ENGRAVE text' feature. You only need to type a sentence and it will be engraved into an object. These will remain separate scripts, but will be offered as a dotG package. Currently there is only the machine controller part.
For older versions: [see the directory listing]
Licence: [GPLv3 (or later if available)]