Foz Meadows of Shattersnipe.com has compiled An A-Z Of Non-Binary Genders. Real-world only and non-insulting, so do not go over there and suggest epicon or scrat.
When I was first planning Requite, it became obvious that there would be people there who didn’t do the gender binary thing. As I suppose most writers do, I’d assumed that humans a couple of thousand years in the future would mostly be like humans throughout the rest of recorded time, with such changes as were necessary for world-building or forwarding the plot. Again, like most writers, I’m not sure I’m doing as well at this as I might, but at least I’m trying. (I even put some sports fans into Heavy Ice, and I’m really not into sports fandom – though while I’m here, congratulations to the England womens cricket team on their Ashes victory!)
I coined epicon from the word epicene, and I always thought I got ‘scrat’ from the big Cassell Dictionary of Slang but it’s not in there, so goodness knows where that came from. I ended up calling Innes ‘it’ throughout the first two books because that’s what Lois McMaster Bujold did with her herms and I thought I’d better follow her example if I wanted to get published, but I’ve moved to ‘they’ from Heavy Ice onwards because calling a person ‘it’ just felt like adding to all the dehumanising crap that people who don’t do the gender binary thing already have to put up with on a regular basis.
People do occasionally ask me whether the epicons think of themselves as third-gender, dual-gendered or genderless, but the rather unhelpful answer is that it depends on the individual epicon.
As for some of the other cultures kicking around in the Requitiverse and their attitudes to gender binaries:
There are transgender KinHarzin and KinHarzin who are temporarily living as a different gender to usual for business or religious reasons. No one thinks this is weird (at least, no one thinks the way their own Clan does it is weird, though they might chunter about the odd ways some other Clans handle it) any KinHarzin over the age of about six has a sophisticated enough understanding of their society and its particular mixture of ‘very stratified and formal’ and ‘utterly cut-throat and manipulative’ to take it in stride. KinHarzin who identify as outside gender binaries tend to leave the KinHarzin as soon as possible. This is because of the KinHarzin’s continued loathing for Nakia Considine, the Barefoot General.
The FSSI want to know what to write on their forms, but other than that are far more concerned about whether people are over or under 25 and whether or not they are lucky enough to have a full work contract.
And the Bind welcomes everybody who fits their genetic criteria. As far as the Bind are concerned, this welcome is mandatory. :)