Constraint Unification Prolog (CUP) developed by the Institute for New Generation Computer Technology (ICOT), Japan. Originally written in C under Unix, MacCup is for Macintosh, DJCup for MS-DOS, with both implementations released as free software.
SET Language 2, close relative of SETL, has some clumsy support for closures, an experimental (broken) object system, and redefines integer division to mean something different than in SETL: 3/2 yields 1.5 in SETL, but only 1 in SETL2.