From the homepage (see below), <strong>Introduction</strong>:

<cite>"OBJ" refers to the language family, while "OBJ2", "_(OBJ3)", 
"_(CafeOBJ)", "_(BOBJ)", etc. refer to particular members of the family. 
The OBJ languages are broad spectrum algebraic specification and 
*(programming language)s, based on order sorted equational logic, 
possibly enriched with other logics (such as _(rewriting|rewrite) 
_(logic), hidden equational _(logic), or first order _(logic)), and 
providing the powerful module system of parameterized programming 
[..]</cite>

<ul class="links">
  <li>_("OBJ Family: OBJ3 CafeOBJ Maude Kumo FOOPS Eqlog"
       | http://www-cse.ucsd.edu/users/goguen/sys/obj.html)</li>
</ul>
