I haven't use BV in many many years, it was an app server in the days before
Java App servers became the most popular. Originally it relied heavily on Iona's 'Orbix' Corba implementation with C and C++ modules. The development environment was server-side JavaScript.
I've heard that it is now
J2EE certified, that is it looks like a Java App server.
One of the main strengths of the BV suite was the custom content management and rules engine, which allowed non technical users to manipluate content on the server. See Broadvision.com for more information