ISETL: Interactive SET Language, distant SETL variant widely used in discrete mathematics: downloads on lower 2/3 of page, for DOS, Mac OS, Windows; source code available.
ISETLW: Interactive SET Language for Windows 9x/Me/NT/2000/XP: downloads, documentation, bugs, sample problems.
SETL Documentation: SET Language: mathematical programming language closely resembling the language of sets and functions used by Mathematicians. Lets users define sets, then define functions and binary operations on the sets: reference documentation for the library of built-in operations.
SETL for Internet Data Processing: A dissertation by David Bacon.
SETL2: 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.
SETLS: FTP site with version 2.2, for PCs using DOS; downloads of self-extracting .exe.