A good tool for collecting mailings, newsletter lists, etc. a lot of possibilities even in the free version. I think it's safe to say that Mailchimp is a veteran in its field and it's holding its own!
Mailchimp is something that alot of people love to hate. It's a fair argument, the product is expensive, the UI is messy, and it has tons of competition. The reason I still use it is that no other email marketing platform has the integrations and features of Mailchimp. The chimp reaches everywhere on the internet, you can't escape it. It has solid features and if you take time to configure it correctly, it will do 99% of what you want.
MailChimp is slowly becoming unsuitable for a wide range of businesses... First of all, the free feature is not efficient anymore. Way too limited. Moreover, the interface for creating and designing newsletters has become more and more user-unfriendly... Don't know where you're headed but I personally don't like it.