ZipShell

Name     ZipShell 
Version  2.1 for OS/2 (8/1998)
Author   Martin Vieregg 
Distrib. Freeware 
Type     REXX CMD/DLL
Price    -
Source   Internet 
         Name: ZipShell*.* 

Description from the author: 

"A handful tiny batchfiles and WP-objects for handling ZIP- and ARJ-files 
with the WPS. Content and unpacking of ZIP and ARJ files. Packing ZIP 
files. With nice icons and REXX programs for installation and 
deinstallation. Freeware. English and German." 

ZipShell is mentioned here because it contains a program called 
SendMsg.EXE. SendMsg can be used to send windows messages to running PM 
Programs and open PM folders. E.g. it' possible to use 

 
SendMsg Programs WM_CLOSE

to close a folder from the command line. 

See IDs for the setup string MENUITEMSELECTED for a list of possible 
windows messages.