The instant messaging app imo has crossed the threshold of a half-billion Play Store installs, and there's a pretty good chance you've never heard of it.

imo was launched by former Googlers way back in 2010, and its claim to fame was offering an instant messaging platform that gathered all of your other messaging accounts in one place. That included AIM (RIP), Skype, Facebook, Google Talk, and yes, even MySpace.

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