Bespoken Tools - Bespoken makes it easy to develop for Alexa, Google Home and Chatbots.
Alexa Skill Kit - Effortless Alexa Skill development with AWS Lambda
BotTalk - Create Alexa skills and Google Assistant actions with Markup
Effct - SAAS platform to help you publish audio content on Alexa
Actions on Google - The open platform for Google Assistant
Alexa Skill Builder by Chatamo - Build your own Alexa skills for free (no code required)!