LLM foremost killer application is what I called context searching whereby it utilized RAG and other techniques to reduce hallucinations and provide relevant results in which arguably ChatGPT is one of the pioneers.
LLM second killer application is for studying for a particular course or subject in which OpenAI ChatGPT is also now providing the service. Probably not the pioneer but most probably one of the significant providers upon this announcement. If in the near future GenAI study assistant can adopt and adapt 3 Blue One Brown approaches for more visualization, animation and interactive learning it will be more intuitive and engaging.
Please check this excellent LLM-RAG AI-driven course assistant at UIUC for an example of university course [1]. It provide citations and references mainly for the course notes so the students can verify the answers and further study the course materials.
[1] AI-driven chat assistant for ECE 120 course at UIUC (only 1 comment by the website creator):