Climbing near the peak of the rankings of late is one service that doesn't fit that mold at all.
It's currently above Uber, Amazon.com and Netflix.
Not that co-founder and CEO Brett Kopf is surprised. His company has 25 million users, including about 35 percent of primary and secondary school teachers. Last year, the app peaked at No. 3 in the Apple store on Aug. 24, adding 315,000 users per day.
As the 2015-16 school year gets going, Kopf is planning for days with up to 400,000 sign-ups."It's so cyclical that we know to the day, the second, it's going to start and we have to scale up our back end to be able to handle that," said Kopf, whose San Francisco-based company recently moved its infrastructure to Amazon Web Services. "There are these days where it just explodes."