Snowflake Pro, the software from Randy Ingermanson, is now free. This used to cost about £100 to buy. Apparently, the burden of requests for more features etc was something he didn't want to deal with.
I found out about this from the following video:
https://www.youtube.com/watch?v=5UdYlEhAuTE
Randy explains why it's free, and the conditions for downloading it here:
https://www.advancedfictionwriting.c...ownload-again/
Basically, you either have to already own an older copy of the software, or to have bought his book (I bought a kindle version of the book from Amazon.)
I haven't tried the software yet as I'm in full flow writing something with Scrivener, which I still haven't taken the plunge to upgrade. I downloaded it and briefly played; Novel Factory (I have the desktop version) does much the same thing, but in a simpler form.
Anyway, someone might find it useful.