you can download it from their link. but everything unique about it, was from 2007. a lot of things have changed on the internet over the past 10 years. also, since ubbfusion was a rip of UBB 6 code, you would technically be going backwards.
in addition, FusionBB is rather dated and may not work with a recent PHP 5 version. there is also no documented support for PHP 7 compatibility at all.
the download of its most current version is on the link above.
