The third party
UBBWiki is our documentation resource, and
UBBDev is our third party modification resource (both owned by myself, a contracted developer for UBB.threads), though note that any modifications to your base system is unsupported by the vendor (UBBSystems).
The UBB.threads software does not have an API that you can tie into; however, there is the
User Authentication Class which allows for a PHP bridge into the software.