Yo

Yo launched on April Fools' Day 2014 and was not a joke. It was built in eight hours. It did one thing: it sent your friends the word "yo." Apple initially rejected it for being too simple. Investors gave it $1 million, then $1.5 million more at a valuation of up to $10 million. Within three months a hacker could pull any user's phone number. FedEx used it to announce packages. The company shut down in 2016. In 2018 the founder opened a Patreon to keep the app running, because an app that says "yo" now needed charity. It was downloaded over 3 million times. Each of those people has to live with that.