Yo-appThere are many ways to say “hello” to your friends:

Hi. Hey there. What’s up? Yo.

Now you can do it on an app – an app that tells your friends “yo.” And that’s it. Nothing more, nothing less. Just “yo.”

The aptly titled “Yo” may sound silly, but it has 50,000 users who have sent more than four million “YOs” since its inception three months ago. An even more interesting fact: YO was built by Or Arbel in just eight hours and it recently garnered $1 million in funding. All so you can say “yo” to your friends (in their defense, it does speak to you in a robotic voice. Robots are cool.).

All you need to do is download the app, type in your phone number, link your contacts, and then BOOM – you can YO anyone you want to. You can even be annoying and keep YOing someone all day long.

If you’re scratching your head in bewilderment, you’re not alone. The app debuted on April Fool’s Day (how apropos) to little fanfare but a lot of skepticism (Apple originally rejected YO because they thought it wasn’t finished) – until tech king Robert Scoble deemed it “the stupidest but most addicting app ever.” From there a star was born.

Or Arbel believes in his product, no matter what anyone else says. First, he moved from his native Israel to San Francisco (which paid off when that $1 million came in), and now he is looking to hire a team of staff and strategic advisors. He’s never been more ready to take his 50,000 users to 50 million.

“The way it affects your life is profound,” he says, adding that people will continue to use it because it will “change their everyday life.”