Smaller than the big platforms and better for it: eleven categories, each of which tells you the exact question it will ask before you commit, in eight languages.
11 gamesUpdate Date Unknown
higherorlower.org
Science and Nature Higher or Lower Games
1 tested
Science data is the most stable in this directory, which makes these games age gracefully and work well in classrooms. The useful distinctions here are unit clarity and difficulty scaling rather than data freshness.
Independent directory. Not affiliated with the games listed.
Platforms covering Science and Nature
Larger sites with science and nature modes among many others.