Back in September 2016, Google purchased Speaktoit, a company specializing in natural language technology. The company's main service at the time was API.AI, an SDK that allowed creating voice interfaces for mobile apps. Google re-purposed the tool to create Google Assistant Apps (formerly known as 'Actions on Google').
API.AI remains the best way for most developers to create Google Assistant actions, but now the service is being renamed to 'Dialogflow'. Google's reasoning is that the service now provides tools outside of a standard API, like analytics features and pre-built agents.
Alongside the name change announcement, the company revealed two new features. The first is an inline code editor, allowing developers to write, test, and implement a functional webhook from the Dialogflow console. The second is multi-lingual agent support, making building apps for multiple languages much easier.
Dialogflow is still completely free for developers to use. You can see the full blog post at the source link below.