You can run it on all 3 platforms (all included in the 1 cost) and it will work on a single file. You can put that on Dropbox or a network share, etc.
This way, you have a central place to manage your wiki but offline. Not a website or saas app,etc.
Does this thing archive web pages for later? Does it compress or dedup the data? What's the appeal, is I guess what I'm driving at. I'm downloading, I'll soon see if it runs on FreeBSD.