If you want to dig a bit and figure out what they use on their forum, you can use your browser dev tools, Sources tab. Example for chrome:
You can find what theme components they use by looking inside /theme-javascripts files. It may not be written explicitly, but there are clues.
For example, this file is from Topic List Thumbnails Theme Component
Plugins are listed in /assets/plugins.
You can also look at the CSS in /stylesheets/:
