Bitrix24 is the only totally free CRM that comes with Mailchimp integration (that we know of). And by free we really mean free – the free version of Bitrix24 is limited by the number of users (12), not by records, meaning it you get unlimited CRM records (leads, clients, companies, deals, quotes, invoices).
To integrate Bitrix24 with Mailchimp, simply use this app. When you use the app, you’ll be able to launch Mailchimp campaigns from inside Bitrix24 and see the statistics there as well. If you don’t don’t have paid Mailchimp subscription and don’t want to get one, you should be aware that Bitrix24 CRM comes with a native free email marketing tool, albeit not nearly as powerful as Mailchimp.
Bitrix24 CRM manual is available here.
If you are interested in buying self-hosted editions of Bitrix24, which come with API, CMS and source code, can be easily customized and integrated with other tools, please download a trial version here.