Alexa Skill Kit - Effortless Alexa Skill development with AWS Lambda
BotTalk - Create Alexa skills and Google Assistant actions with Markup
How To Build Alexa Skills - Step by step of how to build a Alexa Skill for brands
Actions on Google - The open platform for Google Assistant
Alexa Skill Builder by Chatamo - Build your own Alexa skills for free (no code required)!
OK Google - Explore over 150 Google Now voice commands in one place