Eric Yuan, founder and chief executive officer of Zoom Video Communications Inc., center, celebrates during the company's initial public offering at the Nasdaq MarketSite in New York on April 18, 2019. Victor J. Blue | Bloomberg | Getty Images

With people across the country stuck indoors as the coronavirus spreads, they're turning to video calls to chat with friends, family members, colleagues, classmates and customers. There are any number of free services at their disposal, but Zoom is increasingly the one they're choosing. Zoom sits atop Apple's rankings of the most popular free apps in dozens of countries, according to data from analytics company App Annie. Investors love it, at least for the moment. The stock sells for 58 times revenue, compared to a price-to-sales ratio of 8 for Microsoft, and it's gained 26% since Feb. 19, while the S&P 500 has plunged 32% over that stretch. "It's interesting how quickly it's become a verb in Silicon Valley," Jonathan Heiliger, a general partner at Vertex Ventures, which has offices in San Francisco and Palo Alto, California, told CNBC on Thursday. He and his colleagues keep in touch on Zoom. Recently people have also tuned in to weddings, bar mitzvahs and meditation sessions on Zoom. School teachers, musicians and yoga instructors are using it, as are universities, which have gone remote since COVID-19 became a global crisis.

Reliable and easy to use

The question is: Why Zoom? Zoom is known for its reliability, avoiding long outages that discourage repeated use, and it doesn't have the latency that makes some services painful for extended conversations. Unlike Apple's FaceTime for iOS, Zoom is also available on Android and on any laptop. It's also designed to make IT departments comfortable, and people can start video calls for free, as long as they're kept under 40 minutes and below 100 participants. There are also features designed for fun. When you use Zoom, you can upload a picture or a video to create a virtual background. It's so popular that on Thursday Microsoft said it's adding a similar tool to its Teams service. Zoom founder and CEO Eric Yuan has been lauded for the company's efforts to help out schools and other organizations during the crisis. On March 13, Zoom started removing the 40-minute call limit for free accounts at tens of thousands of schools in the U.S. and other countries.