This is a simple
Folder Action Script that will set the executable bit on any file saved within the folder to which the script is attached. Copy and paste the following into a Script Editor document, and save it as a script into your Folder Action Scripts directory.
on adding folder items to thisFolder after receiving theItem
set fileName to POSIX path of theItem
do shell script "chmod +x " & fileName
end adding folder items to
Remember to call your shell (
#!/bin/bash) or application (
#!/usr/local/bin/ruby -w) in the first line of your script. Then save to, or drag your file to, the folder with the action script attached.