What are the important contributions of the Indus civilization to later societies?

The people of the Indus Valley may not have left behind huge monuments like the Egyptian pyramids, but they nonetheless made a significant contribution to civilization. Indus cities were laid out according to a grid pattern, with streets constructed in straight lines and at right angles. This method of town planning is largely taken for granted these days—a quick look at a map of Manhattan will give you some idea of what it looks like—but at the time when Indus civilization reached its peak, this was virtually unheard of.
In relation to town planning, Indus civilization was also renowned for its sanitation system. A sophisticated system of drainage ensured that waste from people's houses was emptied into drains in the street before flowing out of the city.
Indus Valley civilization produced innovations in a number of other areas such as metallurgy, crop cultivation, and the manufacture of clothes. Moreover, its writing system was the first of its kind in South Asia.