The best open-source alternatives you can find today are GPT-NeoX 20B, GPT-J, Bloom, and OPT. But these are all generative models à la GPT-3. In order to turn them into a chatbot you will need to use few-shot learning: https://nlpcloud.com/effectively-using-gpt-j-gpt-neo-gpt-3-a...

These models can be self-hosted but they will require advanced hardware and some specific skills related to AI model deployment.