Movable Type.org

Share takes the simple "email to a friend" idea and lets you completely customize every aspect.

• Include a share form on entries with from, to and message fields
• Use Movable Type template tags to craft your email body and subject however you like
• Send email as plain text or HTML
• Use Movable Type's junk filters to keep spammers out
• A results template lets you provide feedback to the user and match your site's design
• Watch the number of email shares with a dashboard widget, and on the Edit Entry screen

Share Lite, a slightly stripped-down free version is also available.