RenderCalc

RenderCalc is a handy app for animators, 3D artists, and other creative professionals working with video applications such as Cinema 4d, 3DS Max, Blender or Houdini.

Use the number of frames in your scene, and the render time per frame to get an estimate of when your render will finish, along with some handy tips about how you could spend your new found time.

RenderCalc can also notify you when your render should be finished, even when you close the app.