OpenAI with ChatGPT is clearly dominating the space. With 3.7 billion monthly visits worldwide it's usage is now rivaling that of Google's Chrome browser. It's incredible to see how quickly this tool has become so popular, but with it's continued improvement and integration of other GPTs it's become a replacement search engine for many people. 

Others in the market include Google’s Gemini Chatbot with 291.6 million visits in October, the Perplexity chatbot with 90.8 million, Anthropic’s Claude chatbot with 84.1 million, Microsoft’s web-based Copilot website saw 69.4 million visits in October, and lastly, NotebookLM has seen 31.5 million visits in October.