Facebook is planning to merge Messenger, WhatsApp, and Instagram. All three platforms are owned by Facebook, but currently operate in their own space. Merging Messenger, WhatsApp, and Instagram would allow them to operate in the same space together.
A Brief History of Facebook's Messaging Apps
Facebook built Messenger from scratch, making it the social network's only homegrown messaging app. However, Facebook has since acquired Instagram (in 2012) and WhatsApp (in 2014). So all three operate independently of one another. At least for now.
If this plan, reportedly cooked up by Facebook founder and CEO Mark Zuckerberg, comes to fruition, all three apps would share the same underlying technology. This would allow users of any one of the three apps communicate with users of the other two apps.
Mark Zuckerberg Merges Messaging Apps
The New York Times claims Mark Zuckerberg is orchestrating plans to merge Facebook's messaging apps. All three will continue to operate as standalone apps, but by unifying the "underlying technical infrastructure" the platforms will play nicely together.