I maintain a set of modding tools for the Saints Row series of games - they aim to improve on and replace older modding tools that are no longer maintained.
These mod tools are developed using information gathered from reverse engineering the Saints Row titles, and from information provided by Volition.
The source code is available and the tools are freely available to download.
Source code: ThomasJepp.SaintsRow on GitHub
Downloads and more information: Saints Row Mods