WhatsApp - WhatsApp Messenger: More than 1 billion people in over 180 countries use WhatsApp to stay in touch with friends and family, anytime and anywhere.
Thunkable - Powerful but easy to use, drag-and-drop mobile app builder.
BetterChat for WhatsApp - Gorgeous new full-featured WhatsApp client for the Mac.
MIT App Inventor - App Inventor is a cloud-based tool, which means you can create apps for phones or tablets right in your web browser.
Number To Whatsapp - A utility tool which lets your start a Whatsapp conversation without saving the contact of the said person first.
Bubble.io - Building tech is slow and expensive. Bubble is the most powerful no-code platform for creating digital products.