There are many excellent machine learning libraries in various languages — PyTorch, TensorFlow, scikit-learn, PyCaret, etc. The idea is that you can train a model with any tool, language, or framework and then deploy it using another language or application for inference and prediction. For example, let’s say you have a web application built with .Net, an Android app, or even an edge device and you want to integrate your machine learning model predictions into those downstream systems. You can do that by converting your model into ONNX format. You cannot do that with Pickle or PMML format.