Follow Up Boss.

Follow Up Boss has become close to a default for serious agents and teams, and for good reason: it is fast, it gets out of your way, and it routes leads and follow-up with very little friction. The integrations list is deep — it plays nicely with almost every lead source and dialer — and the mobile app is genuinely usable in the car between showings.

It isn't the cheapest option, and it's a CRM, not a marketing engine — it nurtures the leads you already have rather than creating new ones. Paired with a marketing system that fills the top of the funnel, though, it's hard to beat for keeping deals from slipping through the cracks.