WhatsApp Messenger is a cross-platform mobile messaging app which allows you to exchange messages, via Internet, without having to pay for SMS, using a mobile phone.

In addition to basic messaging, WhatsApp users can create groups, send each other unlimited images, video and audio media messages.

yowsup-cli is a command line program, based in python-yowsup library, that allows you to login and use the WhatsApp service, providing all capabilities of an official WhatsApp client, as encryption of messages. This program can be used for multiple purposes as e.g. to receive messages from network servers or appliances, notifying about issues, via direct command or by special agents (Zabbix, Nagios, iwatch, portsentry, etc.).

This package is a good example of the python-yowsup library implementation.