Langchain, Langsmith, Llamaindex, and from Microsoft: Semantick Kernel, Prompt flow. Can someone explain me what each does in the perspective of building an application that uses them all?

Hello,
Senior dev here. Getting into AI quick because I don't want to be one of those devs who are out of the loop of important changes.
I'm currently struggling with getting the picture of what all these puzze pieces do and where they fall in in the big picture.

Let's make as an example a classical angular webapp with a backend API that allows user to load his pdf or make speech to text as data to ingest.
Then …

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