This website's goal is to list significant (or significantly insane) instances of weird sf/f (science fiction/fantasy, also called 'speculative fiction') materials with weird sex. Specifically, I mean works of speculative fiction that feature detailed, fully realized systems of weird sexuality which have significant weight in the story's plot.
When I say systems, I mean that I am looking for materials that feature entire structures of sexual behavior and interaction which are woven into the story as a whole, not single instances of weird, kinky sex. We're talking whole humanoid species with richly detailed mating systems and unique xenobiology, fantasy kingdoms with embedded cultural sexual norms that become integral to a convoluted and shockingly perverse book three plotline, or heavily detailed futuristic sex machines with Ikea-style build instructions that the author is describing one-handed.
There are a few factors which qualify material to be on this list:
The sexual system is not marginalia, it is described in obscene detail.
The author is not trying to hide the sexual system. This thing has a plot you cannot fully explain to an interested party without explaining the weird sex.
What is taken as normal in this story would not be normal on planet earth. Often, it wouldn't be possible. Something technically acheivable by earth humans is fine as long as the story either ratchets it up to 11 or embeds it into its system in a way that a stranger on the street would not just understand without your fervently explaining it to them.
There is also a few bonus factors:
Items which are weak on the main criteria but which have had a certain cultural relevance can be included on the list, especially if the cultural relevance they have had is inspiring others to write more insane sf/f sex. Looking at you, pon farr. Looking. At. You.
Strictly Heterosexual and God-Respecting sf/f sex, even if it has unique worldbuilding, is weak tea. Making your weird sex more gay automatically improves it in every way.
I. Me. The webmaster. If I like something especially, it's more relevant. It's my website.
Some factors that are not taken into consideration are the age of the material, the medium of the material, and whether or not I/you/your deity approves of the content. It does have to be a story, not, for instance, an awesome but unconnected gallery of horny artwork. And I have to have SOME experience with it; if I haven't ever heard of it, there's no way for it to show up on the website!