What are the biggest free chess databases? Is it legal to download games from them? Are there some free chess game databases where it is possible and allowed to download games? Is it possible to use this information for my own purposes? For example, would be allowed to make a machine learning app that learned from the downloaded games?
FICS database

Lichess database

Million base 2.2

PGNMentor

Is it possible to use this information for my own purposes



Absolutely! Nobody has the copyright. Enjoy your machine learning adventure!