Sporcle
"Mentally stimulating diversions"
Zoopz
"Games that make you think"
Wordle
"Wordle is a toy for generating “word clouds” from text that you provide. The clouds give greater prominence to words that appear more frequently in the source text. You can tweak your clouds with different fonts, layouts, and color schemes. The images you create with Wordle are yours to use however you like. You can print them out, or save them to the Wordle gallery to share with your friends."
Word Dynamo
Free study guides and games for word lists.
Free Rice
For each correct answer, ten grains of rice are donated through the World Food Programme to help fight hunger.
Learn4Good
Free online games
National Geographic Games
All subjects