Pascal Briod- Head of Product & Co-Founder, Monito
It has a free tier and is otherwise very cheap in comparison with other services. It still offer a lot of useful features, like triggered messages, API integration, analytics, etc.
Chatra is just a modern take on messaging, more akin to modern mobile messengers. It's light, fast, beautiful and comes with all the bells and whistles small businesses would need AND a robust, well-documented API that allows for fine tuning.