What's the story?
In-depth resources are in the works, but the short version goes like this: while "male" and "female" work well as identities for a large proportion of people, for some of us it's not enough. There are a huge variety of non-binary genders, which run the full range from "all of the above" to "none of the above". Some useful terms are:
Androgyne. Agendered. Non-gender identifying. Polygender. Dual gendered. Genderqueer. Gender non-conforming. Gender questioning. Gender variant. Gender fluid. Butch. Femme. Cross-dressing. Transvestite.
If somebody's gender is non-binary, that doesn't mean that any of the above labels apply to them - and just because one person identifies outside the binary doesn't mean that others who share characteristics with them will. For example, some intersex people have non-binary gender - and others don't.
When it comes right down to it, no-one knows how many non-binary-gendered people there are: when it comes to data collection we're more or less invisible. It's very rare for any options other than "male" and "female" to be offered: see for example our page on the 2011 UK Census.
So that's roughly the size of the problem we're up against - and we'd like you to help. See the links above for ideas as to how...