AdaptBB is a continuation of the original script, now converted to a plugin. This forum software is simple and quick - managing forums has never been so simple and fun.
The AdaptBB plugin is included and installed by default, but if you delete it manually or picked the no-plugin install, then read below:
To install, first download the zip and unpack the folder 'AdaptBB' into your 'app/Old_Plugins' folder - be sure to chmod this new folder to 755. Then login into your admin panel and click on 'Manage Plugins'. You should see this plugin listed and an option to install on the right side. Simply click that and click continue on the install and everything should be done!
Check out the official API Page.