author of llamaindex here:

there's some overlap but our primary use case is going deep into indexing+retrieval for LLM's (and going deep in that area). Not really doing agents/chatbots/prompt management/etc.

E.g. this is a good example of our use cases: https://gpt-index.readthedocs.io/en/latest/use_cases/queries...

You can actually use us as a retrieval/tool in langchain too: https://gpt-index.readthedocs.io/en/latest/how_to/integratio...