Chimpx is a MailChimp integration with MODX Revolution.
From MODX Provider: Install package manager & follow the instructions
Manually:
While installing, you'll be prompted to enter you MailChimp API key (see http://kb.mailchimp.com/article/where-can-i-find-my-api-key/)
You can safely skip this during the install and set/change you API key later by going into the system settings (key = chimpx.apikey).
This is the first steps hopefully leading to a "full" MailChimp integration for MODX Revolution (2.1+).
At this time you can :
Chimpx is distributed as GPL (as MODx Revolution is), but the copyright owner (Romain Tripault) grants all users of Chimpx the ability to modify, distribute and use Chimpx in MODx development as they see fit, as long as attribution is given somewhere in the distributed source of all derivative works.