What does a Hub do?
As the name suggests, a hub allows one or more xAP applications to share a connection to the xAP network on a single PC. This is a technical requirement because of the way PC networks work - by default, only one application can own a network connection on a given port at a time.
There are two variants of hub in common use:
Edward Pearson's .Net 2.0 based hub service for Windows available from here. This hub replaces various earlier hubs based on xAP Framework.Net v1 and v2.
Other Non Dedicated Alternatives
Whilst operating more than a single xAPplication on a single PC requires a Hub to be operational, some xAP aplications offer a built-in hub role if no hub is detected when they start. Applications developed using xAP Framework xFx have this functionality.