We describe RebeCaos: a user-friendly web-based front-end tool for Rebeca, based on the Caos library for Scala. Rebeca is an actor-based language for modelling and analysing concurrent and distributed systems using reactive objects with no shared variables, asynchronous message passing with no blocking when sending and no explicit receiving, and unbounded message buffers for arriving messages. RebeCaos can simulate different operational semantics of (timed) Rebeca, thus facilitating the dissemination and awareness of Rebeca, providing insights into the differences among existing semantics for Rebeca, and supporting quick experimentation of new Rebeca variants (e.g., when the order of received messages is preserved or prioritised). RebeCaos also provides initial reachability analyses for Rebeca models (e.g., the possibility of reaching deadlocks or desirable states).