Whisper Systems

Whisper Systems was an enterprise mobile security company that was acquired by Twitter in November 2011.[1][2] The company was co-founded by security researcher Moxie Marlinspike and roboticist Stuart Anderson in 2010.[3] Some of Whisper Systems' software was made available under free software licenses after the acquisition,[4] which led to the creation of OpenWhisperSystems. https://en.wikipedia.org/wiki/Whisper_Systems

https://en.wikipedia.org/wiki/Open_Whisper_Systems

RedPhone, Text Secure, Signal app https://en.wikipedia.org/wiki/Signal_(software)

Not Whisper Text.