Basically, it's nothing more than a non-playing client. This means I can run it on my Windows server, set up a new, or load, a game and just leave it there for players to log on to and submit their turns. So it could be set to generate new turn automatically every 10 minutes or 24 hours, or it could be set to only generate turn once all orders have been submitted (or by forced turn generation if ie. a player drops out).
I hope you'll give it a second thought, eventually. By leaving out PBEM your're requiring up to 10 players to be online at the same time. This is ok for a fast 15 minute FPS session, but for a longer game as EoS is, it's not really doable.