There is Scala.Rx by Li Haoyi. In short, it aims to be a simpler, easy-to-use and more interoperable reimagination of (parts of) Scala.React.
Don't be misled by the Rx suffix. Scala.Rx has little to do with Reactive Extensions from .NET. Scala.Rx does not focus so much on asynchrony and event streams as rather time-varying values and the expression of functional dependencies with automatic change propagation.