This article recommends a free chatbot app called Perplexity, which supports various search functions such as web search and paper search, and also allows free use of ChatGPT 4.0 with 5 opportunities every 4 hours. Additionally, it has open-sourced large models of LLaMa2 with parameter sizes ranging from 7 billion to 700 billion. Overall, Perplexity is a powerful and free chatbot tool that is highly recommended.