The Sitefinity MailChimp widget from Fenêtre allows you to connect Sitefinity CMS with the popular newsletter tool MailChimp. It is built against MailChimp API version 3.
At Fenêtre we develop ourselves and therefore have made a very developer friendly licence model.
You can download the package for local development and test on all ports of the localhost domain for as many developers as needed for free.
Of course you can also use the package for trial and demo purposes to convince the decision makers ;)