Global site variables to be used in node fields and menu item
Try the Custom Tokens extension to the token module. Here is a quote about it (from the module's project page):

... gives the user the ability to create custom tokens for specific replacements that can improve other modules relying on the Drupal 7 token API or, for Drupal 6, the Token module.
Versions 7.x-1.x and previours relied on PHP evaluation to build custom tokens.
The new 7.x-2.x relies on input filters. While still allowing for PHP tokens through the D7 core PHP filter module, administrators can permit only HTML or plain text custom tokens.