‘M-x goto-address’ is a builtin Emacs feature to highlight all URLs and mail addresses, so that you can browse them or mail them using mouse button-2 (or mouse button-1 starting in Emacs 22). Available in GnuEmacs and XEmacs (in the FSF compat package, I assume).
The library is maintained at GIT:goto-addr.el
This mode will be renamed
‘goto-address-mode’ in Emacs 23.