R10K is a tool that automates the deployment of Puppet modules and environments. The presenter's organization previously used a single monolithic repository to manage all of their Puppet code and hiera data, which led to long test cycles, all-or-nothing deployments, and other issues. They transitioned to using R10K along with separate repositories for each module and hiera data. Now, changes can be tested and deployed independently for each module through a Sinatra-based Git hook that handles dynamic Puppetfile manipulation and environment deployment with R10K.