Google today announced that all developers (and not just those in its private preview program), can start bringing their applications and services to the Google Assistant, starting with what the company calls “conversation actions” on Google Home. This allows developers to create back-and-forth conversations with users through the Assistant and users can simply start these conversations by using a phrase like “OK Google, talk to Eliza.”
Source: Google now lets developers write apps for the Assistant on Google Home | TechCrunch