Choosing which technology should be used to build recommendation engines will depend on the specific task you are trying to accomplish and the technology that you want to use or already use within other services. At nexocode, we have experience using a variety of different programming languages and frameworks, including Python, Keras, TensorFlow, Google Cloud ML Engine, LensKit, and Spotlight. We prefer a technology-agnostic approach to make sure to select the recommendation system techniques, platforms, and libraries that work best for your task.