Just moments ago, we had a post here regarding a product called mydraw. Looked like it was a self-promotion from the author, but, and FWIW, that was OK.
Also note, I made post #5 in this thread, back in 2013.
I went and looked at the support site for the mydraw product. I have not used the Mydraw product myself, so I can't give it a thumbs up or down, in regards to actual usage.
To get to the meat of my post though, at a time in my career when I was solely wearing a network hat, and had to have an extra box on my desktop, to run windows, necessary to run visio for network documentation.
I produced a lot of documentation during that time, and is was all pre-XML visio.
From reading the visio support documentation on the mydraw site, I note a similarity to the omni graffle product, in as much as the visio documents that either product is capable of importing is limited to the newer XML visio documents, and specifically not the pre-xml documents.
This small fact probably isn't relevant to most, but, I have quite a bit of older network diagrams that I occasionally am required to reference, so this feature is relevant to me.