based on an earlier version of the Wolfram Language.
Mathematica immediately allows you to call both standalone programs and individual functions or methods within running programs. Mathematica's architecture allows external functionality to be represented in a symbolic form that can immediately be manipulated within Mathematica—and that often makes access to external functionality from within Mathematica more convenient even than from its own native environment.
Run — run an external command-line program (!prog to run as a shell escape)
RunThrough — feed standard input to an external program and capture output
Compile — automatically generate C code and link back to Mathematica
SystemOpen — open a file, URL, or other target on your computer system
SendMail — send any expression, graphic, etc. by email
LibraryFunctionLoad — load a function from a dynamic library into Mathematica
LibraryFunction — a function that calls into a dynamic library
Install — install a MathLink-installable external program
LinkPatterns — find functions available in a running MathLink program
mprep — externally prepare a MathLink-installable C or C++ program
JavaNew — create a new Java object in any specified class
NETNew — create a new .NET object of any specified type
InstallService — install web services from a WSDL description