I'd like to invite you to rules.io if you are interested. We offer both behavior-based segmentation in Mailchimp to make your campaigns more targeted. And, we offer behavior or inactivity-triggered emails - using Sendgrid and Mandrill is coming to let you use your MC templates. And integration is a Ruby gem for RoR apps or simple REST api.

Let me know if I can personally answer any questions - we're in private beta and want to make sure we're solving problems in the right way! Thanks