I read the Question Is there a way to password protect individual apps? - but the answers focused too much on security issues.
I want to clarify my needs: I use a Software to write my personal diary. I just want to prevent people using my iTunes as a Jukebox and see that interesting icon somewhere and open it.
I don't want to create a special guest account or something like that, and I don't need a mechanism to prevent people from finding my diary files on the filesystem.
I just want to enter a password before the app starts. Is there a freeware solution without using terminal for every launch?