We live in the time of mobile-first development, where many developers keep facing the same problem over and over again: How do we synchronize users’ data across their multitude of devices? Phones can be temporarily offline, tablets only work with WiFi, and browsers may crash. Under no circumstances should users have to resolve merge conflicts, but they do expect history and rollbacks. Can we satisfy all these constraints? “Conflict-free replicated datatypes” are the solution. A rather young technology, poised to solve synchronisation issues once and for all. Come along to a stroll through research & practice of this emerging ecosystem.