Manythings.org is aimed at people studying English as a Second Language or English as a Foreign Language. There are lots of free English language quizzes, word games, word puzzles and other computer assisted English language learning activities. The website is entirely non-commercial and has no advertising.
Although Manythings.org is mostly aimed at ESL students, native English speakers may also find some interesting things on this site. TESL/TEFL teachers may want to recommend this site to their students.
A lot of the activities on the site need flash, but there is also a page which lists items for students using iPhones, iPads and other devices that don't support flash ord java.