The talk given at the FOSDEM conference in 2023 was about building real-time applications with ClickHouse, an open-source analytical database management system. The speaker explained the process of building an analytical application, including where to collect data, how to prepare and clean it, how to load it into ClickHouse, and how to visualize it. They also discussed the use of various technologies such as Apache Flink, Apache Kafka, Apache Spark, and others. The speaker demonstrated loading a large dataset from Wikipedia, analyzing it, and creating real-time dashboards using ClickHouse. They also mentioned the use of modern JavaScript to build their own dashboard instead of using existing tools. The talk highlighted the performance and efficiency of ClickHouse in processing and compressing data, as well as its ability to handle large scale applications. The speaker also mentioned other projects they have worked on using ClickHouse, such as ClickHouse Playground and ClickHouse Testing Infrastructure.