What is the use case of Glow when you have Plutus and why a developer would use it instead of the other smart contract language which is natively supported by Cardano?
From https://glow-lang.org/ :
In other words: what usually takes a huge amount of lines of code, and many experts in various fields, has been automated and abstracted by Glow.
Glow is a higher-level language than Plutus and Solidity. It aims to give developers a way to easily specify the dynamics of a dapp, namely 'who' can do 'what', 'when', and leaves the low-level implementation details to the compiler. Benefits to their approach include the ability to perform formal verification of programs written in Glow, and the ease of auditability of the code (because Glow programs are written much closer to how a person would describe the dapp verbally to another person).
Marlowe is also a high-level language, but provides a smaller, curated set of smart contract building blocks as compared to Glow, to enable non-technical people to draft, write and run their own financial contracts. Marlowe may be useful for a person writing a one-off contract between two people/organisations, while Glow may be useful for a developer who wants to write a dapp used by many people.