The talk given by Russell at the FOSDEM conference in 2023 was about Kotlin Multiplatform and its application in real-world projects. He discussed the basics of Kotlin Multiplatform and how it enables code sharing between different platforms. He also talked about Kotlin Multiplatform Mobile (KMM) and its distinction from Kotlin Multiplatform (KMP). Russell provided examples of Hello World projects and how to get started with Kotlin Multiplatform. He also covered topics such as team structure, modularization, binary size, and API design. Throughout the talk, Russell emphasized the flexibility and adaptability of Kotlin Multiplatform to meet the needs of different teams.