bCNC has been available for a number of years now — when I last looked at it it worked well and it seems to still be under development.
Well, pretty much everything on GitHub is opensource, so you can either dig into the code, or create your own project, or hire someone to make exactly what you want.
Note that Grbl and Super Gerbil are on GitHub: https://github.com/gnea/grbl / https://github.com/paulusjacobus/SuperGerbil so since everything on GitHub is garbage I guess you should give up on it and use something else.
One way to foster development for an opensource project is to put up some money on a site such as Bountysource:
All of the commercial software for controlling Grbl I’m aware of is listed at:
https://wiki.shapeoko.com/index.php/Commercial_Software#Communication.2FControl.2FG-Code_Interpreter