Spark is an email app that offers a Smart Inbox feature to automatically group and prioritize emails. It also includes features such as smart notifications, powerful search, snooze functionality, gatekeeper for spam filtering, send later for scheduling emails, reminders for follow-up communications, and integrations with popular apps like Todoist. Spark's AI-powered features, including the Spark +AI assistant, help users draft emails, create templates, and summarize emails. With its free core features and optional paid plans starting at $4.99/month, Spark can be a valuable tool for individuals looking to manage their inbox more efficiently.