- Kaggle: https://www.kaggle.com/
- Driven Data: https://www.drivendata.org/competitions/
- Crowdanalytix: https://www.crowdanalytix.com/community
- Coda Lab : https://competitions.codalab.org/
- DataScienceChallenge https://www.datasciencechallenge.org/ , but it has shown no activity for long time
- CrowdAI: https://www.crowdai.org/challenges
- Analytics Vidhya https://datahack.analyticsvidhya.com/
- TopCoder: https://www.topcoder.com/challenges, mostly competitive programming challenges, but several data science challenges are available