Alert! The replacement for CanvasX is finally available for those who use Macs. It is now called Canvas Draw, and is on sale until September 15, 2015. (There is also a trial version to test.) Like Adobe's Illustrator, there is a steep learning curve for this graphics software program but it appears to be very versatile. Canvas X was used by a great many people in the needlepoint world until it was dropped. (The current PC version of Canvas X is Canvas 16 but Canvas 15 is also still available.)
While reading the discussion about it on NP Nation, I discovered that Ursa Software also has a stitch diagramming program called StitchGraph that works on both Macs and PCs.
If you are looking for software to create diagrams and charts, Linda K. Reinmuller has a list of programs that might work for you on her blog. It's at the bottom of the page, under "Blog Archive." Thanks, Linda!