Reactive Extensions for Unity that allows LINQ to events and more. This library is free and opensource on GitHub. More info, supports and sourcecodes, see https://github.com/neuecc/UniRx.
This library supports PC/Mac/iOS/Android/WebGL/Windows Store App/etc.

Unity Forums support thread is here, ask me any questions - http://forum.unity3d.com/threads/248535-UniRx-Reactive-Extensions-for-Unity

GameLoop(every Update, OnCollisionEnter, etc), Sensor(like Kinect, Leap Motion, etc) is all of event. Rx considere event as reactive sequence which is possible to compose and perform time-based operations easily by using many LINQ query operators.

In uGUI, UniRx provides Reactive Adapters for Model-View-(Reactive)Presenter Pattern.