Spaced Repetition Websites
wanikani.com
WaniKani is a Japanese radicals, kanji, and vocabulary learning web app that uses mnemonics and SRS to make kanji learning simple.
No data 
$ 8.95
gwern.net
Researcher, self-experimenter, and writer: psychology, statistics, and technology. Categorized list of gwern.net pages.
125,518 $ 88,200.00