A bright yellow powder ingested directly, Rapture is taken as a party drug, but has the unusual effect of increasing the cognitive power of its users, especially with regard to mathemtical calculations. Even a single dose seems to have this effect.
It also creates limited psychic powers, including the ability to psychically attack others, and also creates a limited mindlink between users – a mindlink that can be used to increase the power of the psychic attacks. The mindlink allows access to memories and also the ability for the most heavy users to control the less heavy, effectively over-writing their minds and using them to increase the power of their own mental powers.
It is also powerfully addictive – a single hit is enough to get a user hooked. It was created by a sentient AI, with the intention of controlling humans. Fortunately, it had but one source, a young chemist in Texas who committed suicide while under the effects of the drug. It appears that the effects are temporary, and wear off when the drug is no longer consumed.