CK12 – It s a free website funded by CK-12 Foundation. It’s provide free Online Textbooks , FlashCards, Exercises etc.
You can found that in different learning topics: Arithmetic, Measurement, Algebra, Geometry, Probability, Statistics, Trigonometry, Analysis, Calculus, Life Science, Biology, Physical Science, Chemistry, Earth Science, Physics, Engineering, Technology, English, Astronomy, History, Economics, SAT Exam Prep
You can use your “Google”, “Facebook” or “Twitter” account to sign in.
But, if you just want to take a look. NO sign in required.
Application for Educaiton
The best thing of this site is embeded “Google Translate” that provided into 75 languages!