I'm surprised that no one mentioned Microsoft Powerpoint.... To me, it looks like that was the program it was made with based on the border thicknesses, that all the shapes are readily available in the insert shape menu, and has the same default font as powerpoint.
Even if it was not made with this program, Powerpoint is a great program for simple graphics like the above. I am a student in the engineering/sciences and Powerpoint is widely used for presentations, posters, and papers. The upside is that it's pretty easy to learn and available all over the place
The downside is that it is limited to simpler graphics and it is pretty expensive if you are not planning to use the rest of the programs in Microsoft Office's bundle.
Just a thought, I know this thread is old, but it might help someone somewhere!