lightweight Mailchimp alternative?

Thanks for all the work on this robust Mailchimp integration module. :)

I'm looking for a lightweight alternative for several sites. I need a solution that only does one thing: sends a user's email addresses to MailChimp when they register. Having an unsubscribe link on the user account page would also be great, but it's not a requirement, as people will most likely be unsubscribing directly from the emails.

Do you know of another module that would be suitable, or do you know if there are plans in the works to create one? I'd be more than happy to contribute or review where needed.