HubSpot is a free CRM tool with additional marketing and sales tools in their paid plans. In the free version, all added contacts are included in the same list. The paid marketing and sales tools allow for further contact segmentation.
This HubSpot WordPress plugin automatically adds contacts to HubSpot from your WordPress forms, or updates them if they already exist. If your HubSpot account also has access to contact lists, you can select which list the new contact should be added to. Add HubSpot forms in the sidebar, footer, or in a popup when used with a popup plugin.