WhatsApp is not open-source.
Its source code is not publicly available for reuse, modification, or redistribution, which is a core requirement for software to be considered open-source.
Modified versions like GB WhatsApp are most likely unauthorized clones, developed through possible reverse engineering of the official WhatsApp application.
This ties into a point @vipul once made in response to concerns about people “cloning” a product:
If your IP (source code) is your primary competitive advantage, your business model may be at risk regardless.
read the full comment here: Protecting Open Projects-When Ideas Are Replicated and Sold - #6 by vipul
@Techlinkus u might be interested in this