UniRx
Reactive extensions for Unity
... is a library for composing asynchronous and event-based programs using observable collections and LINQ-style query operators. The game loop (every Update, OnCollisionEnter, etc), sensor data (Kinect, Leap Motion, VR Input, etc.) are all types of events. Rx represents events as reactive sequences which are both easily composable and support time-based operations by using LINQ query operators.