I want to use llama-index in my company

Chains are just functions (kind of a useless abstraction in my mind, hot take? 🌶️ ). If you want to call an LLM or perform some function, you can just do that 🙂 Was there something specific you wanted to do? We have a few features similar to chains for specific functions (most commonly generating structured output)

Depends on what you mean by "custom LLM". If it's an OpenAI-equivilant API, it's pretty easy to change the base url to point to it. Otherwise, you can implement the CustomLLM class
https://docs.llamaindex.ai/en/stable/module_guides/models/llms/usage_custom.html#example-using-a-custom-llm-model-advanced

If you need memory, you can use a chat engine

https://docs.llamaindex.ai/en/stable/module_guides/deploying/chat_engines/root.html

Thanks a lot!! Will give it a try