It depends what you mean by "viable alternatives" and how much money you are prepared to spend on hardware to self-host. As others have mentioned, you can try llama.cpp and LocalAI, but for most ChatGPT-like applications, you won't get anything like as good results. I've found that using GPT-4 via the OpenAI API is somewhat more reliable than ChatGPT, either via the Playground or via a local chat interface like https://github.com/mckaywrigley/chatbot-ui