Cover has hundreds of thousands of users, but it remains unclear what the deal will mean for either Cover or Twitter, with neither company announcing the reason behind the move.
The app, which has been in open beta only since December 2013, is designed to anticipate what smartphone app a user might want to access at any given moment, and adds intelligent shortcuts on the lock screen based on location and app history.
The Cover team said it has now joined San Francisco-based Twitter.
"Twitter, like Cover, believes in the incredible potential of Android," said the Cover team in a blog post on the company's website.
"We built a replacement for Android's default lock-screen that makes our phones easier to use by adapting to our context — providing fast access to the right apps at the right time."
"It’s been an incredible journey, a journey that we’re excited to announce is taking a turn today as we bring the Cover team to Twitter to take these ideas even further," said the post. "So what does this mean for the Cover app? For now, Cover will remain available in the Play Store while we focus our attention on our work at Twitter."
One possible outcome is Twitter will design a full homescreen ecosystem for you phone, like Facebook did with its struggling Facebook Home interface.
Twitter and Facebook are in the midst of a bitter rivalry, with Facebook acquiring popular mobile messaging app WhatsApp for a whopping US$16 billion in February.
Financial terms of the deal between Cover and Twitter were not disclosed, but for now Cover remains in the Play Store.