Apollo.io is a comprehensive, AI-powered sales intelligence and engagement platform that helps B2B sales and marketing teams find leads, automate outreach, and close deals faster by combining a massive B2B contact database with tools for prospecting, email/call sequencing, and pipeline management. It serves as an all-in-one solution, consolidating the typical sales tech stack to streamline lead generation and automate multi-channel campaigns with features like a built-in dialer, AI personalization, and CRM integrations.