Reverse effects are often used to add ambience and atmosphere to sounds, and now Kilohearts has released a plugin that's devoted to them.
Reverser enables you to delay and reverse sections of the input sound, so you can create everything from "hauntingly eerie textures to reverse percussion hits".
It looks like a pretty simple proposition, and you can use it not only as a VST/AU plugin on PC and Mac, but also in one of Kilohearts' Snapin hosts, which enable you to combine effects in a modular manner.
You can buy Reverser on the Kilohearts website for €17.