The talk at the FOSDEM conference in 2023 discussed the use of Kotlin.js in web development. The speaker explored the capabilities of Kotlin.js and showcased examples of websites and data visualizations built with the language. They highlighted the advantages of using Kotlin, such as its safety and reliability, concise syntax, type safety, and code sharing capabilities. Additionally, the speaker discussed the interoperability of Kotlin with Java, JavaScript, TypeScript, Swift, and Objective-C, making it a highly versatile language. They also covered the language design features of Kotlin, including null safety, properties, extension functions, and higher-order functions. Overall, the talk emphasized Kotlin.js as a powerful tool for web development and showcased its potential in various use cases.