[@netweb Keymaster 12 years, 10 months ago]

Dropbox are using the old bbPress ‘Standalone’ 1.x version with some custom theming, though I wouldn’t recommend installing this old version as I am quite sure they have lots of customizations in the backend to get around the known numerous issues with the old version.

Go with the new version https://wordpress.org/plugins/bbpress/installation/

Then start customizing the templates to the style you want
https://codex.bbpress.org/theme-compatibility/