This was recently announced:
https://old.reddit.com/r/CNC/comments/1k08j3y/blockmill_gcode_building_tool/
The introductory video covers the tool quite well:
and it is freely available for use online at:
https://blockmill.github.io/BlockMill/
It includes specific support for:
- facing
- pockets
- rectangular
- circular
- drilling
- slots
with the ability to do:
- grid pattern
- circular array
- repeat
as well as entry strategies for
- helix
- zig-zag
Of especial note is that completed designs may be shared encoded into a URL.
