A new instant messaging app that only allows users to send a single word to their friends is quickly becoming a hot commodity, raising $1 million in two months, US media reported.
The Yo app lets users say "Yo" to their friends, sending them a text notification accompanied by a recorded voice shouting the greeting. But co-founder Or Arbel insisted the deceptively simple app has a lot of potential.
"People think it's just an app that says 'Yo.' But it's really not," Arbel told The New York Times. 
"We like to call it context-based messaging. You understand by the context what is being said."
Arbel said he raised the funds for Yo from a group of investors led by Moshe Hogeg, CEO of image-sharing app Mobli.
Convinced his app has big prospects in line, he left his job as chief technology officer of stock trading platform Stox, which he helped launch last year, and moved from Tel Aviv to San Francisco to focus on Yo.
Arbel said the app could allow newspapers and blogs to notify subscribers that a new article has been published or posted, using a Yo.
Yo is also taking advantage of World Cup frenzy. Any user sending a Yo to "WORLDCUP" will receive a Yo notification when a goal is scored.
Reviews on Apple's App Store were positive, but some delved into sarcasm.
"Yo is a way of life. Since downloading Yo, all my relationships have improved and I've regrown most of my hair," said a reviewer calling himself Nicholas Butler.
News website Think Progress says the app, which took just eight hours to build, now has 50,000 users who have sent about four million Yos.
The company has four part-time employees.
The app is available for free on the iOS and Android operating systems.