BREXX
Free interpreter for Unix, MSDOS, WinCE and Amiga. By Vassilis N. Vlachoudis.
Jaxo: Rexx for Palm OS
Product description, including downloads and free runtime.
KEXX
Dialect used in KEDIT (XEDIT-like editor). Summary by Rex Swain.
PC DOS REXX
PC DOS 2000?s REXX Programming Language
r4
Classic Rexx language interpreter for Windows, from Kilowatt Software.
REXX/imc
Open source Rexx interpreter for Linux/Unix.
REXX/VSE
Product page, including support information and samples.
S/REXX
UNIX implementation from Benaroya. Graphical debugger available.
Shadow/REXX
http://www.neonsys.com/downloads/documentation/Shadow_Web_Server/Shadow%20Web%20Server%20Programming
Dialect used in NEON System's Shadow OS/390 Web Server. Described in "Programming Guide". [PDF]
uni-REXX
An ANSI standard implementation for UNIX systems. Free sample code library.