mc-magento

Mailchimp for Magento 1 Integration. Syncs all data (subscriber, customers, orders, products) and enables marketing automation with email campaigns, automations, ads, postcards and more. Maintained by mailchimp on GitHub, where it has earned 120 stars from the community.

It's actively developed around ecommerce, email-marketing, magento, and is a solid reference for anyone building with these tools.