At the core of RapidPro lies the platform exclusive Flow engine that allows anybody to set up or modify a complex SMS application without the need of a programmer or expensive consulting company. Using basic Android phone, designers and developers can launch their apps instantly in any country in the world while avoiding expensive set-up costs or external technical support. Each interaction in RapidPro is defined by a step. By drawing arrows from one step to another, designers define how users of you application will move through the flow. At any point in the flow designers can trigger actions, such as sending SMS, email or even calling an external API. RapidPro allows to customize messages using information collected from the user allowing for personalized messages and increased response rates.