Executing External Programs from Emacs

[dstein64]

Are there any functions that can launch external programs (not just
command line programs, but also GUI programs) from Emacs? I know that
I can access a shell, and call a program from there, but then emacs is
not operable until I close the program. Prepending the command with
`nohup' is useful, but for some reason it does not work as expected
with all programs, including emacs. I would prefer another way of
doing this - using a specific built-in of emacs lisp if one exists.
Any help would be greatly appreciated. Thanks.