It is marketing that reacts. Instead of a calendar that sends the same email to everyone on day three, the sequence watches what each lead actually does: what they opened, which listings they viewed, which street they keep coming back to, and it fires the next touch off that.
It runs across the channels that reach people: email, SMS, social posting, listing promotion, and retargeting, all from one behavior signal rather than four disconnected tools. The lead who is heating up gets more contact. The lead who is six months out gets kept warm without being burned out.