Hyperopt
Another Python-based hyperparameter optimization library with different algorithmic approaches.
Ray Tune
A scalable hyperparameter tuning library that supports distributed execution and integrates with various ML frameworks.
Scikit-optimize
A simpler optimization library focused on Bayesian optimization for hyperparameter tuning.
SMAC
A tool for algorithm configuration and hyperparameter optimization using Bayesian optimization techniques.
Google Vizier
A proprietary hyperparameter tuning service used internally at Google, not open-source.