MAX Software - MAX/REXX interfaces to DB2, VSAM, PDS and SAM data sets on OS/390. Also REXX extensions. - http://www.maxsoftware.com/
RtoR - REXX to RACF - Development tool kit for RACF (OS/390 Security Server) applications. Access the live RACF database. - http://www.open-softech.com/rtor.htm
REXXTOOLS/MVS - Access to data sets, DB2, APPC and TCP/IP on OS/390. By Open Software Technologies. - http://www.open-softech.com/rexmvs.htm