Alexa Skill Kit - Effortless Alexa Skill development with AWS Lambda
ifttt - IFTTT puts the internet to work for you. Create simple connections between the products you use every day.
Actions on Google - The open platform for Google Assistant
Mycroft.AI - Mycroft is the world’s first open source assistant.
Voice Principles - Guiding principles for voice design, all in one place
Google Assistant - Get things done with Google Assistant