Can more than one user interact with a Shiny Server application concurrently?

Shiny Server launches one R process per application and R itself is single threaded, so requests are serialized. If, for example, it takes 10 seconds to react to a request and 2 people make requests very close to each other; it will likely take ~ 20 seconds for both requests to complete. However, with Shiny Server Pro you can control how many R processes are started for each application and how many connections you want to support per R process.