A real estate CRM (customer relationship management system) is where an agent keeps their leads and contacts and runs long-term follow-up: drip campaigns, pipeline stages, reminders, and history. Follow Up Boss, HubSpot, BoldTrail, Lofty, and Sierra Interactive are common examples.
An open house tool is not a CRM and should not try to be one. Its job is to capture and qualify visitors at the door and hand clean leads to the CRM you already run, so the long follow-up happens where you already work.