Scikit-learn, TensorFlow, and PyTorch are all popular machine-learning frameworks in Python. Scikit-learn is a good choice for beginners and for projects that do not require a lot of customization. TensorFlow is a more complex framework that is better suited for large-scale projects and for deep learning. PyTorch is a newer framework that is similar to TensorFlow in terms of its capabilities, but it is often seen as being more user-friendly and flexible.