The main JOSS site is a Rails application where the submissions are received, the reviews are coordinated and the published papers are listed. It includes dashboards for editors and editors in chief, statistics on published papers and editors activity and configuration options for tracks, papers and feedback among other things.
The source code is available at https://github.com/openjournals/joss
The JOSS app is deployed in Heroku with postgresql and redis as storage options. Live at https://joss.theoj.org
The JOSS docs site includes a section about how to install and configure the JOSS application