I'd like to nominate Fork which allows for parallelizing multiple async functions. I was going to attempt to explain what Fork is, but Zach did a great job on the readme so below is a snippet of that, and said readme also does a great job explaing use cases.
Fork is a Swift library that allows for parallelizing multiple async functions. It provides a Fork struct that takes a single input and splits it into two separate async functions that return different outputs. The two functions can then be merged into one which returns a single output.