I find nicknames which sound different than those of their formalized associates to be intriguing; however this does not mean I am able to list many of them.
Bob /
Bobbie for
Robert - I've used
Bob or
Bobbie as nickname variants.
Jerry for Gerome /
Gerald /
Geraldine
Nate for
Jonathan - I learned of this variation from this site, perhaps from this post.
Tony /
Toni for
Anthony /
Antoine /
Antoinette