One of the cool’s sites I have come across is The Broken Calculator. It involves finding the given numbers using only the keys that are available on the “broken calculator”. This promotes students’ number sense which is important. According to Fennell and Landis’ (1994) chapter, Number and Operation Sense in the book Windows of Opportunity: Mathematics for Students with Special Needs, "[Number sense] is an awareness and understanding about what numbers are, their relationships, their magnitude, the relative effect of operating on numbers, including the use of mental mathematics and estimation" (p. 187). They are suggesting that students must understand how numbers relate to each other. Recognizing these relationships is important for all students, not just for those with special needs.
This cool site also has a timer, which increases motivation through friendly competition amongst the students. Students can also compete against themselves by trying to improve their own times. There are different levels, which provides opportunities for differentiation. Even though this site is not very flashy, I think it is very cool because it helps students to become more proficient in math, while having fun at the same time!!