Besides mechanical CAD/CAM there are several specialized types of software that are optimized for specific tasks such as sign-making, engraving and making jewelry but they tend to be expensive. Most of the reviews and links to cnc related software on this page will tend to be low cost solutions but there are several examples of software in every price range. Unless you are using a CAD\CAM program like Mastercam to generate your gcode, There are four steps to controlling your machine.
1. Create the artwork or drawing for your engraving or part.
2. Save or convert the artwork to a dxf file.
3. Convert the dxf file to gcode.
4. Use step and direction software to control the machine.
What this collection of software allows you to do is create artwork or drawings and then save or convert them to dxf files that can be turned into gcode. The steps listed above are for the CAD\CAM software at the more affordable end of the spectrum. With the more expensive CAD\CAM software you draw your part as a solid or surface then lay the toolpath over it and generate the gcode, there is no dxf file to mess with, unless you import them.