You can call an external program using call-system, call-system-showing-output and open-pipe.
You can call C programs using the FLI. See the LispWorks Foreign Language Interface User Guide and Reference Manual .
On Microsoft Windows a COM/Automation interface is provided. See the LispWorks COM/Automation User Guide and Reference Manual . There is also a DDE interface - see Dynamic Data Exchange.
On Mac OS X an Objective-C API is provided. See the LispWorks Objective-C and Cocoa Interface User Guide and Reference Manual .