From the documentation:

WR-BBS is designed to operate on an IBM PC or compatible micro- computer. It operates as a single-port system, but its database foundation was designed to allow multi-port operation as a potential future development. WR-BBS utilizes the fully-integrated W-TREE Database Manager to rapidly locate and access database records, minimizing the "dead screen" time that would otherwise occur when a database search occurs. The W-TREE Database Manager is integrated at source code level for seamless operation and maximum flexibility for third party developers.