Drift is an instant messaging application that can be integrated into your app. Allowing you to keep up with any issues your user base may be having. With the API you can manage all aspects of your Drift account.
Using the widget API, you can have finer control on how the Drift widget behaves in your app.
The HTTP API enables a developer to track the identities of customers and any events that have occurred on the Drift platform
The terms of service can be located here https://www.drift.com/terms-of-service/