Kaggle

Machine learning competitions were Kaggle's first product and still what the site is most famous for. Companies post problems and machine learners compete to build the best algorithm. Kaggle Kernels is a cloud-based workbench for data science and machine learning that allows data scientists to share code and analysis in Python and R. Over 150K "kernels" (code snippets) have been shared on Kaggle covering everything from sentiment analysis to object detection. Via the Public datasets platform community members share datasets with each other.