IBM Mainframe

CMS/TSO Pipelines
Data flow programming with REXX integration.
http://vm.marist.edu/~pipeline/

FAD-H Software
TSO/REXX functions - DSLIST replacement, global variables and dynamic allocation. Also some TSO utilities.
http://www.btinternet.com/~ashleys/fadh_software.htm

ISPF-L
Mailing list archives, search, and subscription services.
http://listserv.nd.edu/archives/ispf-l.html

MvsHelp
Rexx/CLIST discussion forum.
http://mvshelp.net/vbforums/forumdisplay.php?f=146

Planet MVS
OS/390 freeware and mainframe-related topics by Dave Alcock.
http://www.planetmvs.com/

SSC, Inc.
Assembler Rexx functions for dynamic concat, PDS functions, sleep, WTO(R).
http://www.sscmainframe.com/freeware.htm

Tek-Tips: REXX Technical Help Forum
REXX technical support forum and mutual help system for computer professionals.
http://www.tek-tips.com/threadminder.cfm?pid=277

TSO-REXX
TSO Rexx discussion list, archives and subscription.
http://vm.marist.edu/htbin/wlvindex?TSO-REXX