to poen a local file you just use a link link
<a href="file:///c:\windows\system32\cmd.exe">Open CMD</a>
you can execute exe files, but you'll most likely have to do this with an activeX control.
there are three problems with this approach.
1st, it's IE only,
2nd unsigned activeX controls are blocked from running (so again requires user intervention).
3rd, default IE setup stops activeX opening exe files...
so it is possible, you just need to have set the browser up to do it first!