There are several vector graphics programs out that will work to draft patterns on screen. Adobe Illustrator and Corel Draw are two of the common ones available commercially. Inkscape is an open source free alternative that can also do the job it just depends on your skills and budget.
Personally I use Corel Draw and have since version 4. Corel Draw has come a long way since then and I’m currently using version 12 which I love and fits my budget. The newer versions I’m sure have more bells and whistles but I only need a few tools.
Plain lines
Plain curves
Bezier curves
Shapes variety
Contours
Line thickness
Measurement tools
Node edits
Zoom
Layers
Colors
PDF file formatting
Text both art and paragraph
I’ll go into some of these tools in more depth soon. Illustrator and Inkscape have these common tools as well and there are likely other vector programs that I don’t know about. If you have a favorite drop me a line in the comments below.