This is a lightweight alternative to other newsletter & newsletter-subscription modules.
You can find the Module in the Modules directory and on Github
It can subscribe, update, unsubscribe & delete a user in a list in Mailchimp with MailChimp API 3.0. It does not provide any forms or validation, so you can feel free to use your own. To protect your users, it does not save any user data in logs or sends them to an admin.
This module fits your needs if you...
...use Mailchimp as your newsletter / email-automation tool
...want to let users subscribe to your newsletter on your website
...want to use your own form, validation and messages (with or without the wire forms)
...don't want any personal user data saved in any way in your ProcessWire environment (cf. EU data regulation terms)
...like to subscribe, update, unsubscribe or delete users to/from different lists
...like the Mailchimp UI for creating / sending / reviewing email campaigns
*I have only tested it with PHP 7.x so far, so use on owners risk
EDIT:
Since 0.0.4, instructions and changelog can be found in the README only. You can find it here ?
If you have questions or like to contribute, just post a reply or create an issue or pr on github, thanks!