Many asynchronous programs make use of promises (also known as using light-weight threads or an asynchronous monad) to manage concurrency. I’ve been working on tools to collect trace data from such programs and visualise the results, to help with profiling and debugging.
The diagram below shows a trace from a Mirage unikernel reading data from disk in a loop. You should be able to pan around by dragging in the diagram, and zoom by using your mouse’s scroll wheel. If you’re on a mobile device then pinch-to-zoom should work if you follow the full-screen link, although it will probably be slow. If nothing else works, the ugly zoom buttons at the bottom zoom around the last point clicked.