Our marketing and sales department use Drift to track and engage with our website visitors. We have personalized playbooks so that when a prospect or client from "x" company visits our site, we not only know that they've visited, but we also have targeting messaging towards that account. We are currently trialing the upgraded version where we can watch the live view and see what organization the person is from (based off of their IP address)
Drift also keeps a log of emails opened/read. This is not one of the selling features, as there are other companies that do that much better.