ActiveDemand is a cloud-based marketing automation platform for managing calls, emails and other activity for MQL and integrating into a full-scale CRM for sales process. It has a well-documented API:

https://developers.activedemand.com/

Its data would be a great fit for Fivetran users who use ActiveDemand, like our organization, because it stores granular data about each individual activity (email sent, call received) as well as broader lead scoring trends.