Register application to handle a protocol (alert://something) - in this example typing alert: in browser should run PaintDotNet.exe
Windows Registry Editor Version 5.00
[HKEY_CLASSES_ROOT\alert]
@="URL:alert Protocol"
"URL Protocol"=""
[HKEY_CLASSES_ROOT\alert\DefaultIcon]
@="PaintDotNet.exe,1"
[HKEY_CLASSES_ROOT\alert\shell]
[HKEY_CLASSES_ROOT\alert\shell\open]
[HKEY_CLASSES_ROOT\alert\shell\open\command]
@="\"C:\\Program Files\\paint.net\\PaintDotNet.exe\" \"%1\""