...well, I see several options to do so: each one is "violating" sandbox rules etc. and of course mean a certain risk for the user:
You can use the ActiveX plugin to launch applications. You may use an invisible ActiveX component on the page that serves as command bridge to the applications you may want to start.
What one could do - but what I would never recommend: write a component exectuing command line operations in the front end. But: now you opened the door that unfriendly users may find out, how to manipulate... and do "Command Line" inlining with your application.
What type of application do you want to start from the frontend?