Intercom

Intercom shows you who is using your product (the user's region, browser, local time etc.) and makes it easy to personally communicate with them through targeted, behavior-driven email and in-app messages.

A code snippet inserted in your web or mobile app will create a help widget, which users can use to interact with your support team. Segmentation based on user actions (engagement level, last seen) or attributes (e.g. plan type) lets you send automated email and in-app behavior-driven messages. For instance, when the user first accesses a feature, Intercom can prompt them with more information about it, or solicit feedback.

Intercom integrates with Slack, MailChimp (import users), Stripe and other platforms. It has a powerful API as well.