One way to contribute to REMnux is to add or update the tools that are a part of the distro. To add a new tool:
First become familiar with the way REMnux uses Salt Stack and Debian packages to install and configure tools.
Then consider creating a Salt State file or a Debian package for the tool by following instructions in this section of the documentation site.
If you discovered an issue with an existing REMnux tool, you can help correct it by revising that tool's Salt state file. To do that, follow the instructions for contributing a new state file, but instead of creating a new file, find the state file for the tool and adjust it.