Are there any other open source alternatives to ChatGPT?

Yes, many, huggingface is full of chat-tuned LLaMA derivatives that are supposed to replicate its performance, and tools like text-generation-webui or kobold.cpp can be used to run them with chat-style UX.

But for most tasks none of them come within a mile of GPT-3.5, or within a parsec of GPT-4.

Llamas maybe

Hmm?

"HuggingChat is based on Meta's LlaMA LLM. This has the advantage of access to data collected up to April 12, 2023."

Many.