AWS Redshift is a cloud data warehouse service that can ingest structured and semi-structured data, run SQL queries, and power dashboards and visualizations to enable data-driven insights. It's based on the popular open-source PostgreSQL database application but offers more scalability and cost-efficiency by leveraging cloud data storage and compute resources. In contrast, AWS Athena is a serverless analytics service that lets users run interactive queries against data stored in S3, which can query any type of data that exists in S3 buckets, even if it's unstructured. The main differences between Redshift and Athena include their data structure, location, setup time, partitioning, pricing, and cost-effectiveness. Redshift is more structured and deliberate in handling data queries, while Athena is more flexible and simpler to use. They cater to different use cases, such as event log analytics, real-time analytics, business intelligence, cloud service logs, performance troubleshooting, security data lakes, and S3 data exploration. Knowing which one to use depends on the specific requirements of each project or organization.