Zindex uses the stepping method, and my budding understanding of how the stack context works, to serve as a relatively painless tool for managing z-index. I'm not entirely sure it counts as a library, because it's so damn tiny.
The idea itself came from reading:
Before anything else, clone the repo into your project's Sass directory.
git clone https://github.com/chatrjr/sass-zindex.git
Or grab the tarball/zipball.
Next import Zindex into your project.
@import 'sass-zindex/zindex';
And you're good to go.
To get started using Zindex, check out the example file in the repo. If live demos are you thing, check out the pen with my test cases.