Wikipedia
Pandorabots
Pandorabots, Inc. is an artificial intelligence company that runs a web service for building and deploying chatbots. The Pandorabots Platform is "one of the oldest and largest chatbot hosting services in the world." Clients can create “AI-driven virtual agents” to hold human-like text or voice chats with consumers. Pandorabots implements and supports development of the AIML open standard and makes portions of its code accessible for free under licenses like the GPL or via open APIs.
According to its website, as of December 2015, 225,000+ registered developers have used the platform to create 285,000+ chatbots, logging over three billion conversational interactions with end-users.