Citrix XenApp is a technology that delivers applications to users.
Previous versions were an extension of Microsoft’s Terminal Services, allowing for specific applications installed on a Terminal Server to be available to the users, without giving the users access directly to the desktop. This simplified securing the Terminal Server and made the process easier for users.
In more recent versions Citrix has added Application Streaming, allowing a virtualized application to be sent to the users’ desktop for execution. This allows more applications to be supported, as not all can work in a Terminal Services environment.
In version 5 Feature Pack 2 Citrix is adding the ability to deliver applications that are installed on desktops (virtual or physical), VM Hosted Apps. If the application doesn’t work in Terminal Services and can’t be streamed (not supported by Manufacturer?) then this should do the trick. It does have some drawbacks though. If you want to learn more you can find a great post here.