The Simple Postcard - Text a photo to mail it as a postcard
LoopMessage - LoopMessage is a perfect macOS tool for personalized mass messaging via iMessage/SMS, WhatsApp, Facebook Messenger, Telegram, Viber, and Skype.
Mailjoy - Delightfully easy direct mail marketing. A DIY direct mail tool created for marketing and growth teams. Design, mail & track personalized direct mail postcards and letters. Digital marketers use Mailjoy to send data-driven mail campaigns.
WhatsMany - Send personalised WhatsApp messages in bulk
Felt for iPhone - Handwritten cards for the modern world
Promote Route - A Better WhatsApp™ Experience