This is a plugin for JOSM that allows .atlas files to be opened and visualized.
Clone the project and edit the build.gradle to change the josm version to your JOSM's version:
project.ext.josmVersion = '12484'
Then run:
gradle downloadJosm
and
gradle installPlugin
Open JOSM and navigate to your Plugin Preferences.
Edit > Preferences > Plugins
Type josm-atlas
into the search box and select the plugin.
To contribute to the project, see the contributing guidelines