in TIPS :: 
While there are ways to protect a Delphi application from misusage, there are situation when you want to have the weirdest protection available, but simple to implement.
Here's how to allow only one execution of your Delphi application per Windows session. A warning message appears if a user tries to execute more than once without restarting Windows.
Read the full tip to learn how to create a Windows session trial application ...
Related: Understanding Delphi Project's Source | Protect your Delphi Software | Decompiling Delphi Code
Where is the corresponding GlobalDeleteAtom?
http://blog.delphi-jedi.net/2009/10/26/application-singleton/
@Ipa: thanks for pointing that out. I’ve added a link to your blog post (about mutexes over atoms).